Single-crystal diamond material, single-crystal diamond chip, and perforated tool

ABSTRACT

In a single-crystal diamond material, a concentration of non-substitutional nitrogen atoms is not more than 200 ppm, a concentration of substitutional nitrogen atoms is lower than the concentration of the non-substitutional nitrogen atoms, and the single-crystal diamond material has a crystal growth main surface having an off angle of not more than 20°. A perforated tool includes a single-crystal diamond die, wherein in the single-crystal diamond die, a concentration of non-substitutional nitrogen atoms is not more than 200 ppm, a concentration of substitutional nitrogen atoms is lower than the concentration of the non-substitutional nitrogen atoms, and the single-crystal diamond die has a low-index plane represented by a Miller index of not less than −5 and not more than 5 in an integer, a perpendicular line of the low-index plane having an off angle of not more than 20° relative to an orientation of a hole for wire drawing.

TECHNICAL FIELD

The present invention relates to a single-crystal diamond material, asingle-crystal diamond chip, and a perforated tool. The presentapplication claims a priority based on Japanese Patent Application No.2015-145025 filed on Jul. 22, 2015, the entire content of which isincorporated herein by reference.

BACKGROUND ART

Conventionally, a natural single-crystal diamond has been frequentlyused for a perforated tool, an abrasion-resistant tool, a cutting tool,and the like. Sometimes, a single-crystal diamond synthesized under ahigh pressure has been used. For example, each of Japanese PatentLaying-Open No. 2000-288804 (Patent Document 1), Japanese NationalPatent Publication No. 2000-515818 (Patent Document 2), and JapanesePatent Laying-Open No. 2002-102917 (Patent Document 3) discloses a toolinsert and a wire drawing die, which include: an insert body and a diemain body; and a grindstone chip composed of a natural or artificialdiamond.

A single-crystal diamond is absolutely harder than other materials.Hence, even if any type of diamond is employed for perforated tools,abrasion-resistant tools, and cutting tools, these tools are hardly wornand can be used equally. Actually, they are being used with noparticular problem.

CITATION LIST Patent Document

-   PTD 1: Japanese Patent Laying-Open No. 2000-288804-   PTD 2: Japanese National Patent Publication No. 2000-515818-   PTD 3: Japanese Patent Laying-Open No. 2002-102917

SUMMARY OF INVENTION

In a single-crystal diamond material according to a certain embodimentof the present disclosure, a concentration of non-substitutionalnitrogen atoms is not more than 200 ppm, a concentration ofsubstitutional nitrogen atoms is lower than the concentration of thenon-substitutional nitrogen atoms, and the single-crystal diamondmaterial has a crystal growth main surface having an off angle of notmore than 20°.

In a single-crystal diamond chip according to another embodiment of thepresent disclosure, a concentration of non-substitutional nitrogen atomsis not more than 200 ppm, a concentration of substitutional nitrogenatoms is lower than the concentration of the non-substitutional nitrogenatoms, and the single-crystal diamond chip has a main surface with anoff angle of not more than 20°.

A perforated tool according to still another embodiment of the presentdisclosure includes a single-crystal diamond die, wherein in thesingle-crystal diamond die, a concentration of non-substitutionalnitrogen atoms is not more than 200 ppm, a concentration ofsubstitutional nitrogen atoms is lower than the concentration of thenon-substitutional nitrogen atoms, and the single-crystal diamond diehas a low-index plane represented by a Miller index of not less than −5and not more than 5 in an integer, a perpendicular line of the low-indexplane having an off angle of not more than 20° relative to anorientation of a hole for wire drawing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an exemplary X-ray topography imagefor a crystal growth main surface of a single-crystal diamond materialaccording to an embodiment of the present invention.

FIG. 2 is a schematic cross sectional view showing an exemplary crosssection perpendicular to the crystal growth main surface of thesingle-crystal diamond material according to the embodiment of thepresent invention.

FIG. 3 is a schematic cross sectional view showing another exemplarycross section perpendicular to the crystal growth main surface of thesingle-crystal diamond material according to the embodiment of thepresent invention.

FIG. 4 is a schematic cross sectional view showing a method of producinga single-crystal diamond material according to the embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENTS Technical Problem to be Solved by the PresentDisclosure

With detailed observation, it can be confirmed that perforated tools,abrasion-resistant tools, or cutting tools (such as wire drawing diesand cutting bites), which are considered to have been used in the samemanner, are different from one another in terms of a degree ofoccurrence of large chipping and a wear rate. This is due to thefollowing reason. An act of machining (for example, wire drawing) is aphenomenon taking place with a very complicated mechanism. Hence,particular attention has not been paid to the difference. Specifically,first, workpieces do not have completely the same characteristics. Theworkpieces are slightly varied in characteristics such as elasticmodulus, Young's modulus, hardness, strength, and the like. Moreover, inmachining with machines, motors or pressures or tensions on workpiecesare slightly varied, with the result that pressing forces and pullingforces for the workpieces will be slightly different. When machining isperformed in a dry method, it is considered that the machining isaffected by temperature of chamber and humidity; however, the machiningis not always performed at the same temperature of chamber and the samehumidity. On the other hand, when machining is performed in a wetmethod, there are various types of cooling agents and lubricants andrespective qualities thereof are slightly varied. As such, there arevarious types of parameters related to one another, so that it isconsidered that when a certain parameter is slightly different, wear isgreatly affected. Due to such a complicated phenomenon, these parametersare not intended to be controlled even though it might be recognizedthat wear is greatly affected due to the difference at the side of theperforated tools, abrasion-resistant tools, and cutting tools.

However, large chipping are actually caused in the perforated tools, andabrasion-resistant tools and cutting tools, or large wear rate variationare actually resulted among the perforated tools, abrasion-resistanttools, and cutting tools, disadvantageously. Regarding this, in orderfor manufacturers of workpieces to produce high-quality workpieces withlow cost, it is very important and challenging to manage perforatedtools, abrasion-resistant tools, and cutting tools, exchange the toolswithin an appropriate time, and always produce uniform workpieces.

Therefore, in order to solve the above-described problem, it is anobject to provide a single-crystal diamond material, a single-crystaldiamond chip, and a perforated tool, by each of which occurrence oflarge chipping is suppressed and small wear rate variation is achieved.

Effect of the Present Disclosure

According to the above description, there can be provided asingle-crystal diamond material, a single-crystal diamond chip, and aperforated tool, by each of which occurrence of large chipping issuppressed and small wear rate variation is achieved.

Description of Embodiment of the Present Invention

First, embodiments of the present invention are listed and described.

[1] In a single-crystal diamond material according to a certainembodiment of the present invention, a concentration ofnon-substitutional nitrogen atoms is not more than 200 ppm, aconcentration of substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms, and thesingle-crystal diamond material has a crystal growth main surface havingan off angle of not more than 20°. According to such a single-crystaldiamond material, occurrence of large chipping is suppressed and smallwear rate variation is achieved.

[2] Further in the single-crystal diamond material according to thepresent embodiment, the crystal growth main surface can have an offangle of less than 7°. According to such a single-crystal diamondmaterial, occurrence of large chipping is suppressed and smaller wearrate variation is achieved.

[3] Further in the single-crystal diamond material according to thepresent embodiment, the concentration of the substitutional nitrogenatoms can be less than 80 ppm. According to such a single-crystaldiamond material, occurrence of large chipping is suppressed and smallerwear rate variation is achieved.

[4] Further in the single-crystal diamond material according to thepresent embodiment, a concentration of all nitrogen atoms, which are awhole of the non-substitutional nitrogen atoms and the substitutionalnitrogen atoms, can be not less than 0.1 ppm. According to such asingle-crystal diamond material, occurrence of large chipping issuppressed and smaller wear rate variation is achieved.

[5] Further in the single-crystal diamond material according to thepresent embodiment, an angle of deviation from parallelism between thecrystal growth main surface and a main surface opposite to the crystalgrowth main surface can be less than 2°, the main surface opposite tothe crystal growth main surface can have an undulation with a maximumheight difference Dm of not more than 10 μm/mm, and can have anarithmetic mean roughness Ra of not more than 0.1 μm. According to sucha single-crystal diamond material, control for an off angle of a mainsurface of a chip to be cut out therefrom can be readily performed.

[6] Further in the single-crystal diamond material according to thepresent embodiment, in an X-ray topography image for the crystal growthmain surface, groups of crystal defect points can be gathered, each ofthe crystal defect points being a tip point of a crystal defect linereaching the crystal growth main surface, the crystal defect linerepresenting a line in which a crystal defect exists. According to sucha single-crystal diamond material, occurrence of large chipping issuppressed further.

[7] Further in the single-crystal diamond material according to thepresent embodiment, a density of the crystal defect points can be morethan 2 mm⁻². According to such a single-crystal diamond material,occurrence of large chipping is suppressed further.

[8] Further in the single-crystal diamond material according to thepresent embodiment, a density of combined dislocation points of thecrystal defect points can be more than 2 mm⁻², each of the combineddislocation points being a tip point of a combined dislocation reachingthe crystal growth main surface, the combined dislocation resulting froma combination of at least either of a plurality of edge dislocations anda plurality of screw dislocations. According to such a single-crystaldiamond material, occurrence of large chipping is suppressed further.

[9] Further, the single-crystal diamond material according to thepresent embodiment can include a plurality of single-crystal diamondlayers. According to such a single-crystal diamond material, occurrenceof large chipping is suppressed further.

[10] Further in the single-crystal diamond material according to thepresent embodiment, the crystal defect line can be newly generated orbranched at an interface between the single-crystal diamond layers, anda density of the crystal defect points in the crystal growth mainsurface can be higher than a density of the crystal defect points in amain surface opposite to the crystal growth main surface. According tosuch a single-crystal diamond material, occurrence of large chipping issuppressed further.

[11] Further in the single-crystal diamond material according to thepresent embodiment, a plurality of crystal defect line-like gatheredregions can exist in parallel, and in each of the plurality of crystaldefect line-like gathered regions, groups of the crystal defect pointscan be gathered to extend in a form of lines. According to such asingle-crystal diamond material, occurrence of large chipping issuppressed further.

[12] Further in the single-crystal diamond material according to thepresent embodiment, the concentration of the non-substitutional nitrogenatoms can be not less than 1 ppm. According to such a single-crystaldiamond material, occurrence of large chipping is suppressed further.

[13] Further in the single-crystal diamond material according to thepresent embodiment, when the single-crystal diamond material has athickness of 500 μm, a transmittance for light having a wavelength of400 nm can be not more than 60%. According to such a single-crystaldiamond material, occurrence of large chipping is suppressed further.

[14] In a single-crystal diamond chip according to another embodiment ofthe present invention, a concentration of non-substitutional nitrogenatoms can be not more than 200 ppm, a concentration of substitutionalnitrogen atoms can be lower than the concentration of thenon-substitutional nitrogen atoms, and the single-crystal diamond chipcan have a main surface with an off angle of not more than 20°.According to such a single-crystal diamond chip, occurrence of largechipping is suppressed and small wear rate variation is achieved.

[15] A single-crystal diamond chip according to still another embodimentof the present invention is cut out from the single-crystal diamondmaterial recited in the foregoing embodiment. According to such asingle-crystal diamond chip, occurrence of large chipping is suppressedand small wear rate variation is achieved.

[16] Further in the single-crystal diamond chip according to the presentembodiment, the main surface of the single-crystal diamond chip can be alow-index plane represented by a Miller index of not less than −5 andnot more than 5 in an integer. According to such a single-crystaldiamond chip, occurrence of large chipping is suppressed and small wearrate variation is achieved.

[17] Further in the single-crystal diamond chip according to the presentembodiment, in an X-ray topography image for one of a crystal growthmain surface and a main surface parallel to the crystal growth mainsurface of the single-crystal diamond chip, groups of crystal defectpoints can be gathered, each of the crystal defect points being a tippoint of a crystal defect line reaching one of the crystal growth mainsurface and the main surface parallel to the crystal growth mainsurface, the crystal defect line representing a line in which a crystaldefect exists, and a density of the crystal defect points can be morethan 2 mm⁻². According to the single-crystal diamond chip, occurrence oflarge chipping is suppressed further.

[18] In a perforated tool including a single-crystal diamond dieaccording to yet another embodiment of the present invention, in thesingle-crystal diamond die, a concentration of non-substitutionalnitrogen atoms is not more than 200 ppm, a concentration ofsubstitutional nitrogen atoms is lower than the concentration of thenon-substitutional nitrogen atoms, and the single-crystal diamond diehas a low-index plane represented by a Miller index of not less than −5and not more than 5 in an integer, a perpendicular line of the low-indexplane having an off angle of not more than 20° relative to anorientation of a hole for wire drawing. According to such a perforatedtool, occurrence of large chipping of the single-crystal diamond die issuppressed and small wear rate variation is achieved.

[19] Moreover, a perforated tool according to further another embodimentof the present invention includes a single-crystal diamond die formedfrom the single-crystal diamond chip recited in the foregoingembodiment. According to such a perforated tool, occurrence of largechipping of the single-crystal diamond die is suppressed and small wearrate variation is achieved.

[20] Further in the perforated tool according to the present embodiment,in an X-ray topography image for a crystal growth main surface of thesingle-crystal diamond die, groups of crystal defect points can begathered, the crystal defect points being a tip point of a crystaldefect line reaching the crystal growth main surface, the crystal defectline representing a line in which a crystal defect exists, and a densityof the crystal defect points can be more than 2 mm⁻². According to sucha perforated tool, occurrence of large chipping of the single-crystaldiamond die is suppressed further.

[21] Further in the perforated tool according to the present embodiment,a density of combined dislocation points of the crystal defect pointscan be more than 2 mm⁻², each of the combined dislocation points being atip point of a combined dislocation reaching the crystal growth mainsurface, the combined dislocation resulting from a combination of atleast either of a plurality of edge dislocations and a plurality ofscrew dislocations. According to such a perforated tool, occurrence oflarge chipping of the single-crystal diamond die is suppressed further.

[22] Further in the perforated tool according to the present embodiment,the single-crystal diamond die can include a plurality of single-crystaldiamond layers, and the crystal defect line can be newly generated orbranched at an interface between the single-crystal diamond layers, anda density of the crystal defect points of the crystal growth mainsurface can be higher than a density of the crystal defect points of amain surface opposite to the crystal growth main surface. According tosuch a perforated tool, occurrence of large chipping of thesingle-crystal diamond die is suppressed further.

[23] Further in the perforated tool according to the present embodiment,in the single-crystal diamond die, a plurality of crystal defectline-like gathered regions can exist in parallel, and in each of theplurality of crystal defect line-like gathered regions, groups of thecrystal defect points can be gathered to extend in a form of lines.According to such a perforated tool, occurrence of large chipping of thesingle-crystal diamond die is suppressed further.

[24] Further in the perforated tool according to the present embodiment,in the single-crystal diamond die, the concentration of thenon-substitutional nitrogen atoms can be not less than 1 ppm. Accordingto such a perforated tool, occurrence of large chipping of thesingle-crystal diamond die is suppressed further.

[25] Further in the perforated tool according to the present embodiment,in the single-crystal diamond die, a transmittance for light having awavelength of 400 nm can be not more than 60% when the single-crystaldiamond die has a thickness of 500 μm. According to such a perforatedtool, occurrence of large chipping of the single-crystal diamond die issuppressed further.

Details of Embodiments of the Present Invention First Embodiment:Single-Crystal Diamond Material

With reference to FIG. 1 to FIG. 3, in a single-crystal diamond material20 of the present embodiment, a concentration of non-substitutionalnitrogen atoms is not more than 200 ppm, a concentration ofsubstitutional nitrogen atoms is lower than the concentration of thenon-substitutional nitrogen atoms, and the single-crystal diamondmaterial has a crystal growth main surface having an off angle of notmore than 20°. According to single-crystal diamond material 20 of thepresent embodiment, occurrence of large chipping is suppressed and wearrate variation is small. Here, crystal growth main surface 20 m ofsingle-crystal diamond material 20 refers to a main surface formed bycrystal growth in the single-crystal diamond material. The term “mainsurface of single-crystal diamond material” refers to a main surfacehaving a physical property as the single-crystal diamond material, andincludes crystal growth main surface 20 m, a main surface parallel tothe crystal growth main surface, a main surface 20 n opposite to crystalgrowth main surface 20 m, and the like. It should be noted that whethera main surface of the single-crystal diamond material is one of thecrystal growth main surface, the main surface parallel to the crystalgrowth main surface, and the main surface opposite to the crystal growthmain surface can be identified based on an X-ray topography image forthe main surface and/or a cross section crossing the main surface asdescribed below.

From many factors, the inventors have found impurity variation and planeorientation variation within the single-crystal diamond material asfactors of wear rate variation among perforated tools,abrasion-resistant tools, and cutting tools (for example, wire drawingdies).

However, conventionally, it is difficult to suppress the impurityvariation and the plane orientation variation. For example, when anatural single-crystal diamond is used as a single-crystal diamondmaterial, a plane orientation can be designated; however, an anglecannot be guaranteed with a high precision of not more than 20°.Sometimes, a single-crystal diamond material with a different planeorientation may be introduced. Furthermore, since natural single-crystaldiamonds are formed naturally inside the earth, variation inconcentration of atoms of nitrogen, which is an impurity, is large.Single-crystal diamonds having nitrogen atom concentrations varied by±500 ppm are accepted as the same single-crystal diamond materials.

On the other hand, when an artificial single-crystal diamond formed by ahigh-pressure synthesis method is used as a single-crystal diamondmaterial, a single-crystal diamond with a different plane orientation isnot introduced. However, even when single-crystal diamonds angled off bynot less than 10° are introduced by several/10% or when single-crystaldiamonds angled off by not less than 5° are introduced by several %,they are accepted as the same single-crystal diamond materials.Moreover, although all the prepared single-crystal diamonds do not havean off angle of less than 3° with a probability of 100%, they are allutilized as single-crystal diamonds having a specific plane orientation.Further, nitrogen is naturally introduced into single-crystal diamondmaterials even though the single-crystal diamond materials are obtainedby the high-pressure synthesis method. A certain concentration ofintroduced nitrogen is not guaranteed for the production. Theconcentrations in these single-crystal diamond materials are varied inthe range of 80 to 250 ppm. A variation in the range of ±85 ppm isaccepted.

Thus, not only the natural single-crystal diamond materials but also theartificial single-crystal diamond materials obtained by thehigh-pressure synthesis have variation in atoms of nitrogen, which is animpurity, as well as plane orientation variation. In perforated tools,polishing tools, cutting tools, or the like, wear rates ofsingle-crystal diamond chips or single-crystal diamond dies formed usingsuch single-crystal diamond materials will be varied in the range of 50%to 200% or more (in other words, a wear rate may become 0.5 time or 2.0times as large as an average value of the wear rates).

There are the following approaches to reduce wear rate variation amongsingle-crystal diamond materials. A first approach is to form asingle-crystal diamond material by a vapor phase synthesis method. Inthe high-pressure synthesis method, nitrogen is introduced from a carbonmaterial serving as a source material, a metal material of a solvent, oran atmosphere during the synthesis, and cannot be controlled as a molarunit (based on an amount of molecules as unit). On the other hand,according to the vapor phase synthesis method, a molar ratio of atoms ofa synthesis gas can be controlled. Specifically, the molar ratio of theatoms of the synthesis gas serving as the source material is controlledbased on a gas flow rate in a standard state and an unnecessary(unexpected) gas in a container is reduced to an amount much smallerthan that of the source material gas, thereby controlling to attain auniform concentration of nitrogen atoms in the single-crystal diamondmaterial. Accordingly, variation in concentration of nitrogen atoms dueto the introduction of unexpected gas from the source material, solvent,or synthesis atmosphere can be avoided. However, even when the vaporphase synthesis method is employed, a very small amount of nitrogen gasis introduced from a surrounding atmosphere. Hence, preferably, thesingle-crystal diamond material has a certain concentration of nitrogenatoms or more, rather than absolutely zero. In this case, theconcentration of the nitrogen atoms in the single-crystal diamondmaterial is stabilized. It should be noted that a certain concentrationof nitrogen impurity is not necessarily attained in the material bysetting a certain molar ratio in the synthesis gas. The concentration ofthe nitrogen impurity is dependent on external control factors such aspressure, temperature, and power; however, these factors can becontrolled precisely. The following describes important factors that aredifficult to control.

A second approach is to control the off angle of a main surface of adiamond seed crystal serving as a seed substrate for forming thesingle-crystal diamond material. The off angle of the main surface ofthe diamond seed crystal is a factor that affects introduction of animpurity and that is difficult to precisely control. The off angle ofthe main surface of the diamond seed crystal can be reduced by:determining a plane serving as a reference of angle and cutting using alaser having an excellent degree of parallelization; or calculating adegree of parallelization and cutting using a laser with a correcteddegree of parallelization.

Specifically, although the laser is light with a high parallelism, a cutedge is formed into a wedge-like shape with an angle of several degreesdue to intensity distribution in the radial direction when the laser isused for machining. Moreover, the laser machining is destructivemachining and therefore does not ensure that workpieces are alwaysmachined in the same manner. A maximum height roughness Rz of a machinedsurface becomes not less than 10 μm. Here, maximum height roughness Rzrefers to a maximum height roughness Rz defined in JIS B0601:2013.Moreover, workpieces are adhered to a certain member for the machiningby the laser; however, the workpieces are not always adhered thereto inthe same manner. When adhered, the workpieces are always inclined byseveral degrees. Further, for polishing, the workpieces are removedtherefrom and are then attached to a jig for polishing. Also on thisoccasion, the workpieces are inclined by several degrees. Since polishedsurfaces are rough, finished polished surfaces are inclined by severaldegrees, with the result that the off angles of the main surfaces of theobtained single-crystal diamond materials are varied by not less than20° in total.

In view of these, the present inventors modified a general laser machineuniquely (to change a focal depth out of standard while maintaining adegree of parallelization) in order to attain laser light with a degreeof parallelization of less than 1°, and made a contrivance with regardto intensity in the laser light (by using a uniquely designed DOE lensor the like) in order to attain machining with which a degree ofparallelization (deviation angle from parallelism in the presentspecification) of less than 1° is achieved after machining. Even ifadjustment thereof is insufficient, a degree of parallelization of amachined plate can be less than 1° by correcting the axis of the laserlight by ±1° in the cutting direction for both the surfaces of themachined plate when the degree of parallelization after machining isless than 2°. By this method, a seed crystal having a flat machinedsurface with a maximum height roughness Rz of not more than 5 μm can beproduced. Since a plate-shaped seed crystal produced to securely havesuch flatness and degree of parallelization has a flat surface, no largevariation is caused due to adhesion thereto during polishing, therebyforming a single-crystal diamond material having a main surface with anoff angle of not more than 20° in total. However, more preferably, thesingle-crystal diamond material does not have an off angle of just zero.This is because an off angle of zero leads to substantially no atomicstep to adversely result in instability in an amount of inclusion of animpurity such as nitrogen.

A third approach is to control concentration(s) of non-substitutionalnitrogen atoms and/or substitutional nitrogen atoms in thesingle-crystal diamond material. With attention paid to a differencebetween single-crystal diamond materials due to a difference betweenmanners of introduction of an impurity, the third approach is based onsuch a finding that occurrence of large chipping and a wear rate of asingle-crystal diamond material are affected by a difference between theconcentration of the substitutional nitrogen atoms and the concentrationof the non-substitutional nitrogen atoms among the nitrogen atomsintroduced in the single-crystal diamond material as an impurity.

In single-crystal diamond material 20 of the present embodiment, theconcentration of the non-substitutional nitrogen atoms is not more than200 ppm and the concentration of the substitutional nitrogen atoms islower than the concentration of the non-substitutional nitrogen atoms,thereby suppressing occurrence of large chipping in the single-crystaldiamond material while reducing wear rate variation among thesingle-crystal diamond materials. Moreover, since single-crystal diamondmaterial 20 of the present embodiment is configured to have a mainsurface with an off angle of not more than 20°, plane orientationvariation can be suppressed. Therefore, occurrence of large chipping canbe suppressed while reducing wear rate variation since the concentrationof the non-substitutional nitrogen atoms is not more than 200 ppm, theconcentration of the substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms, and the crystalgrowth main surface has an off angle of not more than 20° insingle-crystal diamond material 20 of the present embodiment.

In single-crystal diamond material 20 of the present embodiment, thenon-substitutional nitrogen atoms refers to nitrogen atoms obtained byexcluding the substitutional nitrogen atoms from all the nitrogen atoms.The concentration of the non-substitutional nitrogen atoms refers to aconcentration obtained by subtracting the concentration of thesubstitutional nitrogen atoms from the concentration of all the nitrogenatoms. Here, the concentration of all the nitrogen atoms is measured bySIMS (secondary ion mass spectrometry method), and the concentration ofthe substitutional nitrogen atoms is measured by ESR (electron spinresonance method).

Although not particularly limited, single-crystal diamond material 20 ofthe present embodiment is preferably formed by the vapor phase synthesismethod. Since a molar ratio of respective atoms in the synthesis gas canbe controlled in the vapor phase synthesis method, the concentration ofthe nitrogen atoms in single-crystal diamond material 20 can becontrolled with higher precision than those in other methods.

In order to reduce the wear rate variation, in single-crystal diamondmaterial 20 of the present embodiment, the concentration of thenon-substitutional nitrogen atoms is not more than 200 ppm, ispreferably not more than 110 ppm, and is more preferably not more than55 ppm.

In order to reduce the wear rate variation, in single-crystal diamondmaterial 20 of the present embodiment, the off angle of the main surfaceis not more than 20°, is preferably less than 10°, is more preferablyless than 7°, is further preferably less than 5°, is still furtherpreferably less than 3°, and is particularly preferably less than 1°.This indicates that the variation becomes smaller as θ, which representsthe off angle, is smaller because binding of carbon in relation withwear resistance is weaken by 1/cos θ and variation thereof is inrelation with the magnitude of differentiation thereof and is thereforesubstantially correlated with sin θ. Moreover, in addition, it is alsoindicated that as the off angle is smaller, the number of steps isdecreased, a probability of including the impurity at the step isreduced, the impurity variation is reduced, and the wear rate variationis reduced. However, when the off angle is zero, the inclusion of theimpurity becomes unstable adversely as described above. Quantitatively,the nitrogen impurity is affected by the number of atomic steps (lineallengths) on the surface determined by the off angle. Since an intervalbetween the atomic steps is proportional to 1/sin θ of the off angle θ,the interval becomes too long (infinite in theory) when θ is zero, withthe result that the impurity is extremely unlikely to be includedtherein. However, when the off angle is 0.005°, the step interval isabout 1 μm, with the result that the impurity is on the order of severalppb as compared with that in the case of the off angle of 5° (severalppm). While not less than 1 ppb of nitrogen is preferably contained intotal in view of the wear rate variation as described above, the offangle is preferably not less than 0.005° and is more preferably not lessthan 0.05° also in view of the wear rate variation. Here, the off angleof the main surface refers to an off angle relative to an arbitrarilyspecified crystal plane. Although the arbitrarily specified crystalplane is not particularly limited, a low-index plane represented by aMiller index of not less than −5 and not more than 5 in an integer ispreferable in order to reduce the wear rate variation. The arbitrarilyspecified crystal plane is more preferably at least one plane having aplane orientation selected from a group consisting of {100}, {110},{111}, {211}, {311}, and {331}.

In single-crystal diamond material 20 of the present embodiment, theconcentration of the substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms in order tosuppress occurrence of large chipping and reduce wear rate variation.This is due to the following reason: when the concentration of thesubstitutional nitrogen atoms is higher than the concentration of thenon-substitutional nitrogen atoms, a wear amount becomes large to resultin large wear rate variation and occurrence of large chipping. Moreover,in single-crystal diamond material 20 of the present embodiment, inorder to reduce the wear rate variation, the concentration of thesubstitutional nitrogen atoms is preferably less than 80 ppm, is morepreferably less than 20 ppm, is still more preferably less than 15 ppm,is further preferably not more than 10 ppm, is still further preferablynot more than 1 ppm, is yet further preferably not more than 0.5 ppm, isparticularly preferably not more than 0.3 ppm, and is most preferablynot more than 0.1 ppm.

In order to suppress large chipping while further reducing the wear ratevariation, in single-crystal diamond material 20 of the presentembodiment, the concentration of all the nitrogen atoms, i.e., the wholeof the non-substitutional nitrogen atoms and the substitutional nitrogenatoms is preferably not less than 1 ppb (0.001 ppm), is more preferablynot less than 0.01 ppm, is more preferably not less than 0.1 ppm, isfurther preferably not less than 1 ppm, and is particularly preferablynot less than 10 ppm. When the concentration of all the nitrogen atomsis less than 0.1 ppb, an amount of naturally introduced nitrogenimpurity becomes unstable to result in a brittle single-crystal diamondmaterial.

In single-crystal diamond material 20 of the present embodiment, inorder to facilitate growth of single-crystal diamond materials havingless varied off angles on a diamond seed crystal and in order tofacilitate control for an off angle of a main surface of a chip cut fromsingle-crystal diamond material 20, an angle of deviation fromparallelism between the crystal growth main surface and the main surfaceopposite to the crystal growth main surface is preferably less than 2°,is more preferably less than 0.1°, and is further preferably less than0.05°. Here, the “angle of deviation from parallelism with the crystalgrowth main surface” means, in a strict sense, an “angle of deviationfrom parallelism with the main surface of the diamond seed crystalduring growth”. Since the main surface of the diamond seed crystal istransferred to the crystal growth main surface in parallel without anychange, equivalency thereof is used. However, when the irregularity ofthe crystal growth main surface thus employing the degree ofparallelization becomes large to result in decreased precision in degreeof parallelization, the crystal growth main surface of thesingle-crystal diamond material is assumed as an initial crystal growthmain surface grown to not more than 100 μm from the main surface of thediamond seed crystal. Since this will appear as a growth stripe, thecrystal growth main surface at the initial stage of the growth becomes astripe pattern when observed by an optical microscope, an SEM (scanningelectron microscope), a CL (cathode luminescence), or a PL(photoluminescence) in cross section. Accordingly, a surface parallelthereto can be evaluated. Hence, when a plate thickness becomes morethan 200 μm, there is employed an angle of deviation from parallelismwith the crystal growth main surface in initial stage of growth within200 μm, preferably 100 μm, and more preferably 50 μm from the mainsurface opposite to the crystal growth main surface. Moreover, in viewof the same as described above, the main surface opposite to the crystalgrowth main surface has an undulation with a maximum height differenceDm of preferably not more than 10 μm/mm, more preferably not more than 5μm/mm, and further preferably not more than 0.6 μm/mm, and has anarithmetic mean roughness Ra of preferably not more than 0.1 μm, morepreferably not more than 50 nm, still more preferably not more than 10nm, further preferably not more than 5 nm, and particularly preferablynot more than 1 nm.

The angle of deviation from the parallelism between the crystal growthmain surface (or the crystal growth main surface at the initial stage ofthe growth) and the main surface opposite to the crystal growth mainsurface of single-crystal diamond material 20 corresponds to an angle ofdeviation between the off angle of main surface 10 m of diamond seedcrystal 10 for growing single-crystal diamond material 20 and the offangle of crystal growth main surface 20 m of single-crystal diamondmaterial 20. Moreover, maximum height difference Dm of the undulation isnot a PV value in a range of several hundred μm, but is a differencebetween the maximum value and the minimum value in a gradual leveldifference of the surface within a range of 1 mm. Maximum heightdifference Dm is not a relative value but is an absolute value based onthe horizontal level of the main surface as a reference while excludingactual inclination of the sample (inclination of the main surface).Maximum height difference Dm can be measured by connecting 0.5-mm visualfields to each other, using a normal surface roughness measuring deviceemploying white interference. Moreover, arithmetic mean roughness Rarefers to arithmetic mean roughness Ra defined in JIS B0601:2013, andcan be measured using a white scanning type white interference typemicroscope (ZYGO provided by Canon).

A small angle of deviation from parallelism between crystal growth mainsurface 20 m and main surface 20 n opposite to crystal growth mainsurface 20 m of single-crystal diamond material 20 ensures a smalldeviation between the off angle of main surface 10 m of diamond seedcrystal 10 and the off angle of main surface 20 n opposite to crystalgrowth main surface 20 m of single-crystal diamond material 20. This isbecause the off angle of main surface 20 n opposite to crystal growthmain surface 20 m of single-crystal diamond material 20 grown on diamondseed crystal 10 does not necessarily precisely coincide with the offangle of main surface 20 n opposite to crystal growth main surface 20 mof single-crystal diamond material 20 removed from diamond seed crystal10 after the growth. When single-crystal diamond material 20 is polishedafter being removed from diamond seed crystal 10 using a laser ofordinary technique, the angle of deviation becomes large to be not lessthan 2° from the parallelism between the main surface of single-crystaldiamond material 20 removed from diamond seed crystal 10 (i.e., mainsurface 20 n opposite to the crystal growth main surface) and crystalgrowth main surface 20 m of single-crystal diamond material 20. In thiscase, it is impossible to finally produce tools with small off anglevariation already at this point of time. Hence, a small angle ofdeviation from parallelism between crystal growth main surface 20 m andmain surface 20 n opposite to the crystal growth main surface isnecessary to produce tools with small off angle variation. Moreover, asmall maximum height difference Dm of the undulation of main surface 20n opposite to the crystal growth main surface ensures small off anglevariation among the main surfaces opposite to the crystal growth mainsurfaces of individual single-crystal diamond chips when cutting thesingle-crystal diamond chips out from the single-crystal diamondmaterial. Although a single-crystal diamond chip is less than 1 mmsquare in many cases, when a surface thereof has an undulation of notless than 10 μm in that size, off angle variation become not less than1° inclusive of portions before and after the undulation. Accordingly,it is also impossible to finally produce tools with small off anglevariation. Hence, a small maximum height difference Dm of the undulationof main surface 20 n opposite to the crystal growth main surface is alsonecessary to produce tools with small off angle variation. In additionto this, a small arithmetic mean roughness Ra of main surface 20 nopposite to the crystal growth main surface is also an necessary,important point.

With reference to FIG. 1 and FIG. 2, preferably in single-crystaldiamond material 20 of the present embodiment, in order to suppressoccurrence of large chipping, in an X-ray topography image for crystalgrowth main surface 20 m, groups of crystal defect points 20 dp aregathered, each of crystal defect points 20 dp being a tip point of acrystal defect line 20 dq reaching crystal growth main surface 20 m,crystal defect line 20 dq representing a line in which a crystal defectexists. Here, the crystal growth main surface refers to a main surfaceformed by crystal growth. Here, in the present invention, the expression“groups of crystal defect points 20 dp are gathered” has a specificmeaning as follows. That is, one group of crystal defect points 20 dp isa collection of a plurality of crystal defect points branched from onestarting point or a collection of crystal defect points branched fromthe foregoing plurality of crystal defect points. A collection ofcrystal defect points branched from a different starting point isconsidered as a different group. Assuming that a minimum circle entirelyincluding one group is expressed as an area of the group, it isexpressed that groups are gathered when the area of a certain group isin contact with or overlaps with the area of another group.

In single-crystal diamond material 20 of the present embodiment,existence of crystal defect points 20 dp and crystal defect lines 20 dqis indicated in an X-ray topography image. Specifically, since thecrystal defect points and the crystal defect lines have higher X-rayreflection intensities than those of the other portions in the crystal(portions with less defects, i.e., portions with high crystallinity),the existence of the crystal defect points and crystal defect lines areshown as dark portions in the case of a positive X-ray topography imageand are shown as bright portions in the case of a negative X-raytopography image. Crystal defect lines 20 dq are shown as the dark orbright portions in the form of lines, whereas crystal defect points 20dp are shown as intersections between a main surface such as crystalgrowth main surface 20 m and crystal defect line 20 dq.

Here, crystal defects 20 d include various types of defects such aspoint defects, dislocations, chippings, cracks, and crystal strains.Moreover, the dislocations include edge dislocations, screwdislocations, and combined dislocations resulting from combinations ofat lease either of a plurality of edge dislocations and a plurality ofscrew dislocations.

Each of crystal defect lines 20 dq constituted of such crystal defects20 d and the like is stopped when a crystal defect line 20 dq is newlygenerated or a crystal defect line 20 dq reaches crystal growth mainsurface 20 m. The tip point of crystal defect line 20 dq reachingcrystal growth main surface 20 m is referred to as “crystal defect point20 dp”. In the present invention, the number of crystal defect points 20dp per unit area is counted to define a density of crystal defect points20 dp. Since it is practically impossible to count not less than 1×10⁴crystal defect points in the present invention, an average value of thecrystal defect points in at least five locations within an arbitraryregion with a limited range may be taken as follows. The crystal defectpoints are counted within the region with a limited range such as aregion of 1 mm square when there are expected to be not less than 10crystal defect points/mm², a region of 500 μm square when there areexpected to be not less than 100 crystal defect points/mm², or a regionof 100 μm square when there are expected to be not less than 1×10⁴crystal defect points/mm². Then, the crystal defect points thus countedare converted into a unit of mm⁻². In doing so, the region in which thenumber of crystal defect points 20 dp is counted must be a regionincluding the crystal defect gathered regions. Here, the crystal defectgathered region refers to a region in which crystal defect points 20 dpare gathered. A crystal defect gathered region extending in the form ofa line is referred to as a “crystal defect line-like gathered region 20r”. If it is unknown which one of the stopped portions of crystal defectline 20 dq reaches crystal growth main surface 20 m, the crystal defectpoint is specified by changing incident angle and diffracting plane fora transmission type X-ray topography image or by capturing a reflectiontype X-ray topography image.

On the other hand, crystal defect line 20 dq is a crystal defect point20 dp at crystal growth main surface 20 m, so that the density of thecrystal defect lines in the vicinity of crystal growth main surface 20 mis equal to the density of the crystal defect points. A crystal defectline exists also inside the crystal and there is an intersection thereofwith an arbitrary surface. The density of such intersections correspondsto the density of the crystal defect lines in the surface. Examples ofthe arbitrary surface include: an interface 212 i between single-crystaldiamond layers 21, 22 grown in the form of layers shown in FIG. 3; asurface parallel to interface 212 i therearound.

Each crystal defect line-like gathered region 20 r is formed by crystaldefect points 20 dp, which are the tip points of crystal defect lines 20dq and which are gathered in the form of lines at crystal growth mainsurface 20 m, each of crystal defect lines 20 dq being a line in whichthe crystal defect exists. Accordingly, crystal defect line-likegathered region 20 r can be shown suitably in an X-ray topography imagemeasured in the transmission type in a direction parallel to the crystalgrowth direction of the single-crystal diamond material (i.e., adirection perpendicular to the crystal growth main surface). Although anX-ray topography image can be measured in the reflection type, thecrystal defect lines are overlapped in the X-ray topography imagemeasured in the reflection type, with the result that it becomesdifficult to discern a state of gathering of the crystal defect points.Since it is necessary to observe the high density of crystal defectpoints in the present invention, it is preferable to use X rays, whichare synchrotron radiation, for the X-ray topography image. For thetransmission type, the measurement is performed using X rays with awavelength of 0.71 Å and (220) diffraction of 2θ=32.9°, for example. Onthe other hand, for the reflection type, the measurement may beperformed using X rays with a wavelength of 0.96 Å and (113) diffractionof 2θ=52.4°. If crystal defect points 20 dp are not discerned asdescribed above, the crystal defect points are specified by capturing animage in a different wavelength and at a different angle of diffraction.Similarly, the measurement may be performed using an X-raydiffractometer of a laboratory system. For example, (111) diffractionmay be observed using a Mo radiation source or (113) diffraction may beobserved using a Cu radiation source; however, a long measurement timeis required to capture an image with high resolution. Although a CCDcamera can be used for the measurement, it is desirable to use a nuclearplate to increase resolution. It is desirable to perform all of storage,development, and fixing of the nuclear plate in a cool environment ofnot more than 10° C. After the development, an image is captured with anoptical microscope to quantify crystal defect points 20 dp and crystaldefect lines 20 dq. Although there is also a method (double-refractionmethod) employing double refraction to measure such crystal defects 20d, some dislocations may not appear in the double-refraction image orpoint defects that are not structure defects may appear in thedouble-refraction image. Hence, the X-ray topography is more preferablethan the double-refraction method.

In single-crystal diamond 20 of the present embodiment, the density ofcrystal defect points 20 dp is preferably more than 2 mm⁻², is morepreferably more than 20 mm⁻², is still more preferably more than 300mm⁻², is further preferably more than 1000 mm⁻², and is particularlypreferably more than 1×10⁴ mm⁻². Since the density of crystal defectpoints 20 dp is more than 2 mm⁻² in such a single-crystal diamondmaterial, occurrence of large chipping is suppressed due to stressrelaxation provided by the high density of the crystal defect linescorresponding to the high density of the crystal defect points.Particularly, chipping resistance is particularly excellent when thedensity of crystal defect points 20 dp is more than 1000 mm⁻².

In single-crystal diamond material 20 of the present embodiment, thedensity of the combined dislocation points of crystal defect points 20dp is preferably more than 2 mm⁻², is more preferably more than 30 mm⁻²,is further preferably more than 300 mm⁻², and is particularly preferablymore than 3000 mm⁻². Each of the combined dislocation points is a tippoint of a combined dislocation reaching the crystal growth mainsurface, the combined dislocation resulting from a combination of atleast either of a plurality of edge dislocations and a plurality ofscrew dislocations. Since the density of the combined dislocationpoints, which are the tip points of the combined dislocations reachingthe crystal growth main surface, is more than 20 mm⁻² and the effect ofstress relaxation provided by the combined dislocations is large in sucha single-crystal diamond material, occurrence of large chipping issuppressed further. Particularly, chipping resistance is particularlyexcellent when the density of the combined dislocation points is morethan 300 mm⁻².

Here, the combined dislocations can be observed by changing an X-raydiffraction direction (g vector) in the X-ray topography. For example,when observing, in the transmission type, the (001) plane that is acrystal plane of the diamond single crystal, the edge dislocations canbe observed in a g vector of a [440] direction and cannot be observed ina g vector of a [4-40] direction or the like orthogonal to the foregoingg vector, whereas the combined dislocations can be observed in aplurality of g vectors of the [440] direction, the [4-40] direction, andthe like orthogonal to one another. It should be noted that whenobserving other dislocations having a Burgers vector that is notperpendicular to the <001> direction, in which the dislocations, i.e.,the crystal defect lines extend and that has a component also in the<001> direction, such dislocations can be observed in the reflectiontype in g vectors of the [044] direction, the [004] direction, the [111]direction, the [113] direction, and the like, for example. However, inthe case of the reflection type, the crystal defect lines such as thedislocations are overlapped with one another in the image, with theresult that it becomes difficult to discern whether or not the crystaldefects are in the form of the structure of the present invention. Sincethe combined dislocations thus observed are also crystal defect lines,the density of the combined dislocations can be measured in the samemanner as the measurement for the density of the crystal defect lines.

With reference to FIG. 3, single-crystal diamond material 20 of thepresent embodiment preferably include a plurality of single-crystaldiamond layers 21, 22. Since the single-crystal diamond materialincludes the plurality of single-crystal diamond layers 21, 22,occurrence of large chipping is further suppressed.

With reference to FIG. 3, first single-crystal diamond layer 21 is grownby CVD (chemical vapor deposition) on a main surface 10 m of a diamondseed crystal 10 having seed crystal defect line-like gathered regions inwhich groups of seed crystal defect points 10 dp are gathered to extendin the form of lines at main surface 10 m, and crystal defect lines 21dq transferred from the defects of seed crystal defect points 10 dp atmain surface 10 m extend in first single-crystal diamond layer 21 in thecrystal growth direction. In second single-crystal diamond layer 22grown by CVD on first single-crystal diamond layer 21, crystal defectpoints 20 dp are tip points of crystal defect lines 22 dq that havedefects transferred from defects of crystal defect lines 21 dq and thatextend in the crystal growth direction to reach crystal growth mainsurface 20 m of single-crystal diamond material 20.

On this occasion, generally, in first single-crystal diamond layer 21, aplurality of crystal defect lines 21 dq are transferred from one seedcrystal defect point 10 dp of diamond seed crystal 10, and in secondsingle-crystal diamond layer 22, a plurality of crystal defect lines 22dq are transferred from one crystal defect line 21 dq of firstsingle-crystal diamond layer 21. Hence, as the number of single-crystaldiamond layers 21, 22 is increased, the number of crystal defect points20 dp of single-crystal diamond material 20 is increased. As a result,the structure becomes such that as the number of single-crystal diamondlayers 21, 22 is increased, the number of crystal defect lines 21 dq, 22dq from main surface 20 n opposite to crystal growth main surface 20 mtoward crystal growth main surface 20 m is increased, thereby obtaininga crystal having higher chipping resistance.

Preferably in single-crystal diamond material 20 of the presentembodiment, crystal defect lines 21 dq, 22 dq are newly generated orbranched at interface 212 i between single-crystal diamond layers 21,22, and the density of crystal defect points 20 dp of crystal growthmain surface 20 m is higher than the density of the crystal defectpoints of main surface 20 n opposite to crystal growth main surface 20m. According to such a single-crystal diamond material, occurrence oflarge chipping is suppressed further.

With reference to FIG. 1, preferably in single-crystal diamond material20 of the embodiment, in an X-ray topography image for a certain mainsurface (for example, crystal growth main surface 20 m), a plurality ofcrystal defect line-like gathered regions 20 r exist in parallel, and ineach of crystal defect line-like gathered regions 20 r, groups ofcrystal defect points 20 dp are gathered to extend in the form of lines,each of crystal defect points 20 dp being a tip point of a crystaldefect line 20 dq reaching at least one surface (for example, crystalgrowth main surface 20 m) of single-crystal diamond material 20, crystaldefect line 20 dq representing a line in which crystal defect 20 dexists. Occurrence of large chipping is suppressed in the single-crystaldiamond material. Here, the form of lines can be determined based on anabrupt decrease of probability of existence of crystal defect points 20dp on a line rotated by a certain angle φ (for example, not less than10° and not more than 90°) from one fixed line having a certain width ascompared with probability of existence of crystal defect points 20 dp onthe fixed line. That is, when at least five lines are extracted andangles and crystal defect points on lines are plotted in a graph, a peakappears with the fixed line being centered, thereby determining the formof lines.

Here, crystal defect line-like gathered regions 20 r each have a lengthL, and have an interval D in the direction in which they extends in theform of lines. Moreover, the plurality of crystal defect line-likegathered regions 20 r exist in parallel with each other at a pitch P. Alarger length L of crystal defect line-like gathered region 20 r is morepreferable. Length L of crystal defect line-like gathered region 20 r ispreferably not less than 300 μm, and is more preferably not less than500 μm. A smaller interval D between crystal defect line-like gatheredregions 20 r is more preferable. Interval D is preferably not more than500 μm and is more preferably not more than 250 μm. A smaller pitch Pbetween crystal defect line-like gathered regions 20 r is morepreferable. Pitch P is preferably not more than 500 μm, and is morepreferably not more than 250 μm. Moreover, pitch P may not be constant.Moreover, the direction in which crystal defect line-like gatheredregions 20 r extends in the form of lines refers to an average ofdirections in which the plurality of crystal defect line-like gatheredregions 20 r extend in the form of lines. The direction in which eachcrystal defect line-like gathered region 20 r extends in the form of aline preferably forms an angle θ of not more than 30° relative to theaverage of the directions.

In single-crystal diamond material 20 of the present embodiment, theconcentration of the non-substitutional nitrogen atoms is preferably notless than 1 ppm, is more preferably not less than 3 ppm, is still morepreferably not less than 5 ppm, is further preferably not less than 8ppm, is still further preferably not less than 10 ppm, and isparticularly preferably not less than 30 ppm. Since thenon-substitutional nitrogen atoms in single-crystal diamond material 20are joined to crystal defect lines 20 dq, occurrence of large chippingin single-crystal diamond material 20 is suppressed, thus increasingchipping resistance. Particularly, when the concentration of thenon-substitutional nitrogen atoms is not less than 10 ppm, excellentchipping resistance is exhibited. When groups of crystal defect points20 dp are gathered, a larger amount of non-substitutional nitrogen ismore likely to be formed in the diamond to provide high chippingresistance. The concentration of such non-substitutional nitrogen atomscan be calculated by subtracting the concentration of the substitutionalnitrogen atoms measured by ESR (electron spin resonance method) from theconcentration of all the nitrogen atoms measured by SIMS (secondary ionmass spectrometry method).

In single-crystal diamond 20 of the present embodiment, a transmittancefor light having a wavelength of 400 nm when the thickness ofsingle-crystal diamond material 20 is 500 μm is preferably not more than60%, is more preferably not more than 30%, and is further preferably notmore than 10%, and is particularly preferably not more than 5%. Further,a transmittance for light having a wavelength of 600 nm when thethickness of single-crystal diamond material 20 is 500 μm is preferablynot more than 60%, is more preferably not more than 30%, and is furtherpreferably not more than 10%, and is particularly preferably not morethan 5%. When the transmittance for light having a wavelength of 400 nmis small, there are a multiplicity of crystal defect lines in thesingle-crystal diamond material of the present embodiment and there arealso a large amount of non-substitutional nitrogen in the single-crystaldiamond material of the present embodiment, whereby crack is suppressedand chipping resistance is exhibited. When a transmittance for lighthaving a longer wavelength of 600 nm is small, there are a multiplicityof crystal defect lines in the single-crystal diamond material of thepresent embodiment and there are also a large amount ofnon-substitutional nitrogen in the single-crystal diamond material ofthe present embodiment, whereby crack is suppressed and chippingresistance is exhibited. Only with such a multiplicity of crystal defectlines, the transmittance for light does not necessarily have a largeinfluence; however, when the non-substitutional nitrogen is combinedwith the crystal defect lines (such that the non-substitutional nitrogenenters a space between crystal defect lines and the crystal defect linesextend between the nitrogen atoms), the non-substitutional nitrogen andthe crystal defect lines are synergically increased and a sp2 componentof carbon therearound is increased slightly, thus affecting thetransmittance for light. The crystal defect lines and thenon-substitutional nitrogen thus combined have an influence to preventspread of crack and chipping. Hence, the transmittance for light in thatcase serves as a good index for chipping resistance.

Here, the “transmittance for light” refers to a substantialtransmittance for incoming light, rather than a transmittance thereinexcluding reflectance. Hence, even when there is no absorption orscattering, the transmittance will be about 71% at maximum. A convertedvalue of transmittance in the case of a different thickness can beobtained using a generally known formula in consideration of multiplereflections therein. Moreover, the “transmittance for light when thethickness of the single-crystal diamond material is 500 μm” refers to atransmittance for light measured when the thickness thereof is 500 μm,or a transmittance of light obtained by measuring a transmittance oflight measured when the thickness thereof is not 500 μm and convertingthe measured transmittance into a transmittance when the thickness is500 μm.

Second Embodiment: Single-Crystal Diamond Chip

In a single-crystal diamond chip according to the present embodiment, aconcentration of non-substitutional nitrogen atoms is not more than 200ppm, a concentration of substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms, and thesingle-crystal diamond chip has a main surface with an off angle of notmore than 20°. With such a single-crystal diamond chip, small wear ratevariation is achieved. Generally, a single-crystal diamond chip isadvantageous in production in the following point: the single-crystaldiamond chip is obtained by cutting the single-crystal diamond materialperpendicularly to the main surface thereof and values of off angles atboth sides are the same. However, a main surface of a single-crystaldiamond material generally has a large off angle due to suppression ofpoly-crystallization or the like in the synthesis. Therefore, even whenthe off angle of the main surface is large, in order to reduce wear ratevariation, it is effective to cut a single-crystal diamond chip out fromthe single-crystal diamond material obliquely by the off angle such thatthe off angle of the main surface of the single-crystal diamond chipbecomes not more than 20°. In view of this, the off angle of the mainsurface is preferably less than 10°, is more preferably less than 7°, isstill more preferably less than 5°, is further preferably less than 3°,and is particularly preferably less than 1°.

The off angle variation among the single-crystal diamond chips dependson the off angle variation among the single-crystal diamond materials. Asmaller off angle of the single-crystal diamond material is morepreferable because the off angle of the single-crystal diamond chip canbe more likely to be reduced when the off angle of the single-crystaldiamond material is smaller. Moreover, the variation is more likely tobe reduced as described above when a difference is smaller (for example,not more than) 5° between the off angle of the crystal growth mainsurface of the single-crystal diamond material (or the crystal growthmain surface at the initial stage of the growth) and the off angle ofthe main surface of the single-crystal diamond chip. When the differenceis more than 5°, the variation tends to be increased to exceed an offangle of 10°. However, finally, wear variation among final products moredepends on the off angle of the main surface of the single-crystaldiamond chip as compared with the off angle of the crystal growth mainsurface of the single-crystal diamond material. Therefore, the off angleof the main surface of the single-crystal diamond chip takes precedenceover the off angle of single-crystal diamond material. Here, the mainsurface of the single-crystal diamond chip refers to a surface mainlyperforming a function as a tool when mounted on the tool irrespective ofits size. For example, in the case of a perforated tool, the mainsurface is a main surface supposed to perform perforation. In the caseof a cutting tool, the main surface is a main surface supposed to serveas a cutting face.

However, when it is difficult to specify a tool, the main surface isbased on the following definition. The main surface of thesingle-crystal diamond chip refers to a surface having a highersymmetry, rather than a surface having the maximum area. In the case ofa cylinder, the main surface is a circular surface. In the case of arectangular parallelepiped or a quadrangular prism, the main surface isa surface closer to a square. When each of the surfaces is close to asquare within an error of 8%, the main surface is each of a pair ofsurfaces having a higher degree of parallelization. In the case of acube, any surface can be assumed as the main surface because the crystalstructure of the diamond is a face-centered cubic structure and the offangle is therefore the same for all the surfaces.

Moreover, the single-crystal diamond chip according to the presentembodiment is cut out from the single-crystal diamond of the firstembodiment. Therefore, the single-crystal diamond chip according to thepresent embodiment refers to each of single-crystal diamond chips havingsubstantially polygonal prism shapes (having substantially polygonalmain surfaces), such as a single-crystal diamond chip having asubstantially quadrangular prism shape, a substantially square prismshape, a substantially rectangular parallelepiped shape, or asubstantially cubic shape, or refers to each of single-crystal diamondchips having substantially cylindrical shapes (having substantiallycircular main surfaces). The term “substantially” is used to indicate ashape that can be seen so when viewed by eyes, rather than a strict,precise shape. Precision is expected to be about less than ±10%.Therefore, the off angle of the single-crystal diamond material is notnecessarily equal to the off angle of the single-crystal diamond chip.Moreover, basically, the single-crystal diamond chip is preferablytranslationally symmetrically cut out from the single-crystal diamondmaterial in order to use the material efficiently. With such asingle-crystal diamond chip, smaller wear rate variation is achieved.

The single-crystal diamond chip of the present embodiment is produced bycutting the single-crystal diamond material; however, the off angle andthe like uniform in the single-crystal diamond material will be variedwhen just cutting it. Therefore, it is preferable to use a laser havinga degree of parallelization of not more than 2°. The degree ofparallelization of such a laser is more preferably not more than 1°, isfurther preferably not more than 0.5°, and is particularly preferablynot more than 0.2°. The degree of parallelization is attained by acontrivance such as modification of an optical system by taking aprecedence over focal depth. By employing such a fact that the laserprovides a wedge-shaped cut shape, control for ¼ of the angle (0.05°)can be further attained by changing the cutting direction for the sidesfacing each other. With such a technique, the off angle of the mainsurface of the single-crystal diamond chip can be controlled to be aless varied angle.

Furthermore, a single-crystal diamond chip having a highly symmetricalshape such as a cubic shape is not suitable because a surface to be usedis not distinguishable. A rectangular parallelepiped shape or a shapehaving different height, width, and length is preferable because asurface to be used is distinguishable. However, a cubic shape orrectangular parallelepiped shape provided with a mark is preferablebecause a surface to be used is distinguishable. The cutting by thelaser may be performed perpendicular or oblique to a surface orperpendicular or oblique to a side as long as the degree ofparallelization is attained. With these contrivances, the single-crystaldiamond chip can be produced in which the nitrogen atom concentrationand the off angle are controlled.

In the single-crystal diamond chip of the present embodiment, the mainsurface of the single-crystal diamond chip is preferably a low-indexplane represented by a Miller index of not less than −5 and not morethan 5 in an integer. With such a single-crystal diamond chip, smallerwear rate variation is achieved. Here, in view of the above, thelow-index plane is at least one plane having a plane orientationselected from a group consisting of {100}, {110}, {111}, {211}, {311},and {331}.

Preferably in the single-crystal diamond chip of the present embodiment,in an X-ray topography image for one of the crystal growth main surfaceand the main surface parallel to the crystal growth main surface (thismain surface is a main surface formed by cutting the single-crystaldiamond material; the same applies to the description below), groups ofcrystal defect points are gathered, each of the crystal defect pointsbeing a tip point of a crystal defect line reaching one of the crystalgrowth main surface and the main surface parallel to the crystal growthmain surface, the crystal defect line representing a line in which acrystal defect exists, and the density of the crystal defect points ismore than 2 mm⁻². Occurrence of large chipping is suppressed in thesingle-crystal diamond chip. Moreover, the crystal growth main surfaceand the main surface parallel to the crystal growth main surface of thesingle-crystal diamond chip are not particularly limited but arepreferably parallel or perpendicular to the main surface of thesingle-crystal diamond chip in order to suppress occurrence of largechipping of the single-crystal diamond chip.

In the single-crystal diamond chip of the present embodiment, atransmittance for light having a wavelength of 400 nm when the thicknessof the single-crystal diamond chip is 500 μm is preferably not more than60%, is more preferably not more than 30%, and is further preferably notmore than 10%, and is particularly preferably not more than 5%. Further,a transmittance for light having a wavelength of 600 nm when thethickness of single-crystal diamond material 20 is 500 μm is preferablynot more than 60%, is more preferably not more than 30%, and is furtherpreferably not more than 10%, and is particularly preferably not morethan 5%. When the transmittance for light having each of thesewavelengths is small, there are a multiplicity of crystal defect linesin the single-crystal diamond material of the present embodiment andthere are also a large amount of non-substitutional nitrogen in thesingle-crystal diamond material of the present embodiment, whereby crackis suppressed and chipping resistance is exhibited. Here, since thesingle-crystal diamond chip is made smaller than the single-crystaldiamond material, it is effective to perform measurement using aspectrophotometer of a general microscope. An entrance surface and anexit surface for light are preferably polished optically evenly in orderto avoid scattering at the surfaces as much as possible.

Third Embodiment: Perforated Tool

In a perforated tool including a single-crystal diamond die according tothe present embodiment, in the single-crystal diamond die, aconcentration of non-substitutional nitrogen atoms is not more than 200ppm, a concentration of substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms, thesingle-crystal die has a low-index plane represented by a Miller indexof not less than −5 and not more than 5 in an integer, and an off angleof a perpendicular line of the low-index plane is not more than 20°relative to an orientation of a hole for wire drawing. With such aperforated tool, occurrence of large chipping in the single-crystaldiamond die is suppressed while achieving small wear rate variation.

Moreover, the perforated tool according to the present embodimentincludes the single-crystal diamond die formed from the single-crystaldiamond chip of the second embodiment. According to such a perforatedtool, small wear rate variation among single-crystal diamond dies isachieved.

The single-crystal diamond die included in the perforated tool of thepresent embodiment is produced from the single-crystal diamond chip ofthe second embodiment. Since the single-crystal diamond chip has atleast one or more flat surfaces, a hole for wire drawing in a certaindirection can be formed based on the surface(s) as a reference whenproducing the perforated tool (here, each of the reference surfaces isbasically a main surface of the single-crystal diamond chip; however, ahole may be formed in a surface different from the surface defined asthe main surface of the single-crystal diamond chip). For example, theflat surface is aligned with a surface on which the single-crystaldiamond chip is placed when producing the die. When the surface isvaried, holes of perforated tools are varied with respect to the planeorientation. Based on the rectangular parallelepiped shape, aninappropriate surface is avoided from being set. Although the shape ispreferably of different length, width, and length, a rectangularparallelepiped shape including a square or a cubic shape can be used ifit is not mistaken by providing a mark (a point provided by a laser or agraphite layer surface). According to the above method, thesingle-crystal diamond die can be produced from the single-crystaldiamond chip in which the nitrogen atom concentration and the off angleof the main surface are controlled.

Preferably in the perforated tool of the present embodiment, in an X-raytopography image for the crystal growth main surface of thesingle-crystal diamond die, groups of crystal defect points aregathered, each of the crystal defect points being a tip point of acrystal defect line reaching the crystal growth main surface, thecrystal defect line representing a line in which a crystal defectexists, and a density of the crystal defect points is more than 2 mm⁻².In such a perforated tool, occurrence of large chipping of thesingle-crystal diamond die is suppressed. Moreover, the crystal growthmain surface of the single-crystal diamond die is not particularlylimited but is preferably parallel or perpendicular to the direction ofthe hole of the single-crystal diamond die in order to suppressoccurrence of the large chipping of the single-crystal diamond die.

In the perforated tool of the present embodiment, a density of combineddislocation points of the crystal defect points is preferably more than2 mm⁻², each of the combined dislocation points being a tip point of acombined dislocation reaching the crystal growth main surface, thecombined dislocation resulting from a combination of at least either ofa plurality of edge dislocations and a plurality of screw dislocations.In such a perforated tool, occurrence of large chipping of thesingle-crystal diamond die is suppressed.

Preferably in the perforated tool of the present embodiment, thesingle-crystal diamond die includes a plurality of single-crystaldiamond layers, a crystal defect line is newly generated or branched atan interface between the single-crystal diamond layers, and the densityof the crystal defect points in the crystal growth main surface ishigher than the density of the crystal defect points of the main surfaceopposite to the crystal growth main surface. According to such aperforated tool, occurrence of large chipping of the single-crystaldiamond die is suppressed.

Preferably in the perforated tool of the present embodiment, a pluralityof crystal defect line-like gathered regions exist in parallel in thesingle-crystal diamond die, and in each of the plurality of crystaldefect line-like gathered regions, groups of the crystal defect pointsare gathered to extend in the form of lines. According to such aperforated tool, occurrence of large chipping of the single-crystaldiamond die is suppressed.

Preferably in the perforated tool of the present embodiment, theconcentration of the non-substitutional nitrogen atoms is not less than1 ppm in the single-crystal diamond die. According to such a perforatedtool, occurrence of large chipping of the single-crystal diamond die issuppressed.

In the perforated tool of the present embodiment, in the single-crystaldiamond die, a transmittance for light having a wavelength of 400 nmwhen the single-crystal diamond die has a thickness of 500 μm ispreferably not more than 60%, is more preferably not more than 30%, isfurther preferably not more than 10%, and is particularly preferably notmore than 5%. Furthermore, a transmittance for light having a wavelengthof 600 nm is preferably not more than 60%, is more preferably not morethan 30%, is further preferably not more than 10%, and is particularlypreferably not more than 5%. According to such a perforated tool,occurrence of large chipping of the single-crystal diamond die issuppressed.

Fourth Embodiment: Method of Producing Single-Crystal Diamond Material

With reference to FIG. 4, a method of producing single-crystal diamondmaterial 20 of the present embodiment includes: a step (FIG. 4 (A)) ofpreparing diamond seed crystal 10 having seed crystal defect gatheredregions in which seed crystal defect points 10 dp are gathered at mainsurface 10 m; and a step (FIG. 4 (B)) of growing single-crystal diamondmaterial 20 by chemical vapor deposition on main surface 10 m of diamondseed crystal 10. Seed crystal defect point 10 dp refers to a seedcrystal defect point 10 dp at main surface 10 m of diamond seed crystal10. The seed crystal defect gathered region refers to a region in whichcrystal defect points are gathered at main surface 10 m of diamond seedcrystal 10. In the seed crystal defect gathered region at main surface10 m of diamond seed crystal 10, groups of seed crystal defect points 10dp are more preferably gathered, seed crystal defect points 10 dp arefurther preferably gathered to extend in the form of lines, and seedcrystal defect points 10 dp are particularly preferably seed crystaldefect line-like gathered regions, in which groups of seed crystaldefect points 10 dp are gathered to extend in the form of lines.

In the method of producing single-crystal diamond 20 of the presentembodiment, seed crystal defect points 10 dp, the seed crystal defectgathered region, and the seed crystal defect line-like gathered regionare shown suitably in an X-ray topography image measured in thetransmission type in the direction perpendicular to main surface 10 m ofdiamond seed crystal 10 (i.e., X-ray topography image for main surface10 m of diamond seed crystal 10).

(Step of Preparing Diamond Seed Crystal Having Seed Crystal DefectGathered Regions)

With reference to FIG. 4 (A), the step of preparing diamond seed crystal10 having seed crystal defect gathered regions in which seed crystaldefect points 10 dp are gathered at main surface 10 m of diamond seedcrystal 10 is not particularly limited; however, in order to effectivelyprepare diamond seed crystal 10 having seed crystal defect line-likegathered regions in which groups of seed crystal defect points 10 dp aregathered to extend in a form of lines at main surface 10 m of diamondseed crystal 10, the step can includes: a sub step of preparing diamondseed crystal 10; a sub step of forming the seed crystal defect gatheredregion in which seed crystal defect points 10 dp are gathered at mainsurface 10 m of diamond seed crystal 10; and a sub step of forming aconductive layer region 10 c at main surface 10 m of diamond seedcrystal 10 by implanting ions to break and convert the diamond intographite in the ion implantation region.

In the sub step of preparing diamond seed crystal 10, as diamond seedcrystal 10, there is prepared a type Ib single-crystal diamond or typeIIa single-crystal diamond grown by the HPHT(high-pressure/high-temperature) method, or a single-crystal diamondgrown by CVD using the type Ib single-crystal diamond or the type IIasingle-crystal diamond as a seed crystal.

In the sub step of forming the seed crystal defect gathered regions inwhich seed crystal defect points 10 dp are gathered at main surface 10 mof diamond seed crystal 10, various types of defect points are includedin seed crystal defect points 10 dp, such as seed crystal defect points,seed crystal dislocation points 10 dd (tip points of dislocationsreaching main surface 10 m, such as edge dislocations, screwdislocations, and combined dislocations resulting from combinations ofat least either of a plurality of edge dislocations and a plurality ofscrew dislocations), seed crystal chipping points 10 dv, seed crystalcracking points, and seed crystal damage points 10 di. Moreover, theseed crystal defect gathered region is preferably formed by performingmechanical polishing using a grindstone at a rotation speed of 500 rpmto 3000 rpm and a load of 0.5 kgf to 50 kgf, for example. In thegrindstone, diamond abrasive grains having an average grain size of 9 μmto 35 μm are fixed using a metal. The seed crystal defect points aremore readily formed in the main surface of the seed crystal as theaverage grain size is larger, the rotation speed is larger, and the loadis larger. The load falls within the range of 0.5 kgf to 50 kgf. Theload is preferably not less than 0.5 kgf, is more preferably not lessthan 5 kgf, is further preferably not less than 10 kgf, and isparticularly preferably not less than 20 kgf.

As the load is larger, a mechanism for suppressing vibration isnecessary in order to avoid breakage of a substrate. On the other hand,a high frequency of vibration is permitted. This leads to generation ofminute cracks at the surface of diamond seed crystal 10, thuscontributing to forming starting points of the groups of seed crystaldefect points 10 dp. When diamond seed crystal 10 is rotated in thepolishing direction, seed crystal defect points 10 dp are more likely tobe formed to be gathered. On the other hand, when diamond seed crystal10 is fixed, seed crystal defect points 10 dp are more likely to beformed to be gathered in the form of lines. Since the diamond seedcrystal is broken readily when the load is large, the thickness of thediamond seed crystal needs to be increased with respect to the size ofthe diamond seed crystal. For the thickness of the diamond seed crystalwith respect to the size of the diamond seed crystal, a thickness of notless than 0.8 mm with respect to a square of 4 mm is preferable when theload is not less than 0.5 kgf and less than 5 kgf, a thickness of notless than 1.6 mm with respect to a square of 4 mm is preferable when theload is not less than 5 kgf and less than 20 kgf, and a thickness of notless than 3.2 mm with respect to a square of 4 mm is preferable when theload is not less than 20 kgf. By increasing slowly and carefully a loadincrease rate when applying the load, the diamond seed crystal can bepolished without being broken even if it is out of the above range;however, this is time consuming. By also performing reactive ion etching(ME), microwave plasma etching, ion milling, or the like after themechanical polishing, the density of the generated seed crystal defectpoints can be finely adjusted and the effect thereof is substantiallymaintained.

Moreover, a minute crack can be formed at a location where diamond grownfrom the left and diamond grown from the right hit each other whensynthesizing diamond to fill a groove formed in the diamond usingphotolithography and etching technique or using a laser. However, it ispreferable that the direction of the off angle and the direction of thegroove are parallel to each other in a range of ±10°. If the directionof the off angle and the direction of the groove are not parallel toeach other in the above range, particularly, if they are almostperpendicular to each other, the groove is completely filled anddisappears, with the result that the minute crack providing the effectof the present invention is not obtained. In this case, even if reactiveion etching, plasma etching, or ion milling is performed up to the depthof the formed groove in order to form the minute crack, the effect ofthe present invention cannot be obtained.

The sub step of forming conductive layer region 10 c at the main surface10 m side of diamond seed crystal 10 can be performed by implanting ionsinto the main surface 10 m side of diamond seed crystal 10 to form anion implantation region. For the ions to be implanted, carbon ions,nitrogen ions, silicon ions, or phosphorus ions are used preferably.

(Step of Growing Single-Crystal Diamond Material)

With reference to FIG. 4 (B), the step of growing single-crystal diamondmaterial 20 is performed by growing single-crystal diamond material 20on main surface 10 m of diamond seed crystal 10 by CVD (chemical vapordeposition). As the CVD, microwave plasma CVD, DC plasma CVD, hotfilament CVD, and the like are used suitably. For gases forsingle-crystal growth, hydrogen, methane, argon, nitrogen, oxygen,carbon dioxide, and the like are used to adjust the concentration of thenon-substitutional nitrogen atoms (the concentration obtained bysubtracting the concentration of the substitutional nitrogen atoms fromthe concentration of all the nitrogen atoms) in the single-crystaldiamond material to be preferably not less than 1 ppm, more preferablynot less than 3 ppm, still more preferably not less than 5 ppm, furtherpreferably not less than 8 ppm, still further preferably not less than10 ppm, or particularly preferably not less than 30 ppm. Further, adoping gas may be added, such as diborane, trimethylboron, phosphine,tertiary butylphosphorus, or silane. The crystal growth main surface ofsingle-crystal diamond material 20 preferably has a plane orientation of(100). In a region in which the thickness of single-crystal diamondmaterial 20 is 1 μm to 7 μm at the initial stage of the crystal growth,it is preferable to grow it under conditions that at least a growthparameter (α) is not less than 2 and the temperature of diamond seedcrystal 10 is not more than 1100° C. The growth parameter (α) hereinrefers to a value obtained by multiplying, by square root of 3, a ratioof the rate of crystal growth in the <100> direction to the rate ofcrystal growth in the <111> direction.

The thickness of single-crystal diamond material 20 to be grown is notparticularly limited but is preferably not less than 300 μm and is morepreferably not less than 500 μm in order to suitably form a cuttingtool, a polishing tool, an optical component, an electronic component, asemiconductor material, and the like. The thickness of single-crystaldiamond 20 is preferably not more than 3 mm and is more preferably notmore than 1.5 mm in order to prevent cracks from being generated due tostress with diamond seed crystal 10. In the case of growingsingle-crystal diamond material 20 having a thickness of more than 1 mm,it is preferable to grow second single-crystal diamond layer 22 on firstsingle-crystal diamond layer 21 as an additional single-crystal diamondmaterial 20 after growing first single-crystal diamond layer 21 having athickness of not more than 500 μm and then removing diamond seed crystal10 as described below.

It should be noted that in the case of growing single-crystal diamondmaterial 20 including the plurality of single-crystal diamond layers 21,22 as shown in FIG. 3, first single-crystal diamond layer 21 and secondsingle-crystal diamond layer 22 can be continuously grown on diamondseed crystal 10 as single-crystal diamond material 20. However, in thecase of growing single-crystal diamond material 20 having a largethickness (for example, thickness of more than 1 mm), it is preferablethat first single-crystal diamond layer 21 having a thickness of notmore than 500 μm is grown, then the diamond seed crystal is removed, andthen second single-crystal diamond layer 22 is additionally grown, inorder to prevent diamond seed crystal 10 from being broken due to stressresulting from the large thickness of single-crystal diamond material20. Between the formation of first single-crystal diamond layer 21 andthe formation of second single-crystal diamond layer 22, the environmentis returned from a growth environment to a normal atmosphere at a roomtemperature and then is changed to the growth environment again.Accordingly, the crystal defect lines previously formed in the presentinvention are more likely to be branched, thus increasing the crystaldefect points. Meanwhile, the above-described mechanical polishing canalso be performed onto the crystal growth main surface of firstsingle-crystal diamond layer 21. In that case, first single-crystaldiamond layer 21 serves as a new seed substrate to become a diamond seedcrystal 10 shown in FIG. 3, thereby achieving growth with increasednumber of initial start points.

(Step of Removing Diamond Seed Crystal)

With reference to FIG. 4 (C), in order to obtain single-crystal diamondmaterial 20 efficiently, the method of producing single-crystal diamondmaterial 20 of the present embodiment can further include a step ofremoving diamond seed crystal 10.

In order to remove diamond seed crystal 10 efficiently, in the step ofremoving diamond seed crystal 10, it is preferable to remove diamondseed crystal 10 by performing electrochemical etching such aselectrolytic etching to decompose and remove conductive layer region 10c that is the ion implantation region formed by performing ionimplantation into diamond seed crystal 10.

(Step of Additionally Growing Single-Crystal Diamond Material)

With reference to FIG. 4 (D), in order to obtain single-crystal diamondmaterial 20 in which occurrence of large chipping is further suppressed,the method of producing single-crystal diamond material 20 in thepresent embodiment can further include a step of additionally growing asingle-crystal diamond material 20.

The step of additionally growing single-crystal diamond material 20 isperformed by growing second single-crystal diamond layer 22 by CVD onthe main surface of first single-crystal diamond layer 21, which issingle-crystal diamond material 20 having been already grown. In firstsingle-crystal diamond layer 21, crystal defect lines 21 dq havingdefects transferred from seed crystal defect points 10 dp of mainsurface 10 m of diamond seed crystal 10 extend in the crystal growthdirection as shown in FIG. 4 (C). In second single-crystal diamond layer22 grown by CVD on first single-crystal diamond layer 21, crystal defectpoints 20 dp are tip points of crystal defect lines 22 dq that havedefects transferred from crystal defect lines 21 dq and that extend inthe crystal growth direction to reach crystal growth main surface 20 mof single-crystal diamond material 20.

On this occasion, generally, in first single-crystal diamond layer 21, aplurality of crystal defect lines 21 dq are transferred from one seedcrystal defect point 10 dp of diamond seed crystal 10, and in secondsingle-crystal diamond layer 22, a plurality of crystal defect lines 22dq are transferred from one crystal defect line 21 dq of diamond seedcrystal 10. Hence, as the number of single-crystal diamond layers 21, 22is increased, the number of crystal defect points 20 dp ofsingle-crystal diamond material 20 is increased, thereby furthersuppressing occurrence of large chipping.

EXAMPLES Example 1

(Production of Samples)

1. Preparation of Diamond Seed Crystal

With reference to FIG. 4 (A), each of type Ib single-crystal diamondswas prepared as diamond seed crystal 10. The type Ib single-crystaldiamond was grown by the HPHT (high-pressure/high-temperature) methodand had a main surface with an off angle of 2° relative to a (001) planein the <100> direction. The type Ib single-crystal diamond had a size of4 mm×4 mm and had a thickness shown in Table 1.

The main surface of each of diamond seed crystals 10 was polished usinga grindstone at a rotation speed of 500 rpm to 3000 rpm under a loadshown in Table 1 (specifically, 10 kgf to 20 kgf or 0.5 kgf to 5 kgf).In the grindstone, diamond abrasive grains having an average grain sizeof 9 μm to 35 μm are fixed by a metal. Here, for the polishing,attention was paid to selection of polishing directions, and thereforeTable 1 shows the polishing directions distinctively. “Fixation” inTable 1 indicates a general polishing method (with a small load) inwhich the single-crystal diamond material is fixed and polished suchthat a grinder moves in a direction in which the polishing is relativelyreadily performed (for example, substantially the <100> directionrelative to the (100) plane). “Rotation→Fixation” indicates a method inwhich a substrate made relatively flat by a general method is polishedfor 2 hours while being rotated (turned) and then is fixed and polishedfor 1 hour. With this, defects are likely to be introduced in the formof lines. The load during the polishing in Table 1 is a load in the caseof “Fixation” or “Rotation→Fixation”. Thus, as the seed crystal defectline-like gathered regions in which crystal defect points were gatheredin the form of lines, scratches were formed to extend in the <100>direction in the form of lines in each of Example 1-1 to Example 1-3,whereas scratches with interspersed crystal defect points were formed ineach of Example 1-4 and Example 1-5. Here, the load was applied in thefollowing manner: the load was gradually increased at a rate of not morethan 3 kgf/min while using an apparatus having a mechanism forsuppressing vibration of the grindstone not to exceed 110% of themaximum value of the above range of the load.

Next, the densities of seed crystal defect points 10 dp and seed crystaldamage points 10 di were adjusted by dry-etching the main surface of thediamond seed crystal using oxygen (O₂) gas and carbon tetrafluoride(CF₄) gas. It should be noted that the average grain size refers to anaverage grain size designated by a manufacturer that supplies a diamondgrinder, and the average grain size herein refers to an average particlesize in the specification of a grinder provided by International DiamondInc. Such an average grain size is generally determined by screeninggrains using a sieve. An average grain size of 35 μm to 9 μm correspondsto grain sizes screened by a sieve of #600 to #1500 (sieve of 600 to1500 per inch).

Furthermore, in each of Example 1-2, Example 1-3, and Example 1-5,photolithography was employed to form grooves each having an aspectratio of 2, a groove width of 3 μm, and a groove interval of 200 μm asshown in Table 1, and then CVD growth was performed without addingnitrogen.

Next, carbon ions were implanted into main surface 10 m of each diamondseed crystal 10 with an energy of 300 keV to 10 MeV at an dose amount of1×10¹⁵ cm⁻² to 1×10¹⁸ cm⁻², thereby forming conductive layer region 10c. This step was performed when removing the single-crystal diamondmaterial, grown through vapor phase method, from the diamond seedcrystal by electrolytic etching. This step was omitted in the case wherethe diamond would be sliced by a laser in a subsequent step.

2. Formation of Single-Crystal Diamond Material

Next, with reference to FIG. 4 (B), microwave plasma CVD (chemical vapordeposition) was employed to grow single-crystal diamond 20 on mainsurface 10 m of each diamond seed crystal 10 provided with the seedcrystal defect line-like gathered regions. For crystal growth gases,hydrogen (H₂) gas, methane (CH₄) gas, and nitrogen (N₂) gas were used.The concentration of the CH₄ gas relative to the H₂ gas was set at 5 mol% to 20 mol %, and the concentration of the N₂ gas relative to the CH₄gas was set at 0 mol % to 5 mol %. A crystal growth pressure was set at5 kPa to 15 kPa, and a crystal growth temperature (temperature of thediamond seed crystal) was set at 800° C. to 1200° C.

3. Removal of Diamond Seed Crystal

Next, with reference to FIG. 4 (C) and FIG. 4 (D), respectivesingle-crystal diamond materials 20 were removed from diamond seedcrystals 10 by performing electrolytic etching to decompose theconductive layer regions in the diamond seed crystals. Alternatively, inthe case where no ion implantation had been performed, slicing wasperformed using a laser to remove them from the diamond seed crystals.The removed-side surface (main surface opposite to the crystal growthmain surface) of each single-crystal diamond material obtained by theion implantation and the subsequent electrolytic etching had anundulation with a maximum height difference Dm of not more than 1 μm/mmand an arithmetic mean roughness Ra of not more than 10 nm, which weremeasured using a white scan type white interference type microscope(ZYGO provided by Canon). In the case where the single-crystal diamondmaterial was sliced using a laser, the single-crystal diamond materialneeded to be polished after the removal. The polished, removed-sidesurface (main surface opposite to the crystal growth main surface) ofthe single-crystal diamond material had an undulation having a maximumheight difference Dm of not more than 1 μm/mm and an arithmetic meanroughness Ra of not more than 10 nm. Since arithmetic mean roughness Rawas not more than 10 nm, an influence of scattering could be eliminatedin transmittance evaluation. In the case of the removal using a laser,the degree of parallelization thereof needed to be reduced as small aspossible and a spread width thereof needed to be taken intoconsideration in order to eliminate a deviation between the growthsurface and the removed-side surface. After the polishing, theelimination of deviation needs to be maintained and was maintained to benot more than 0.5°. For the removal using the ion implantation, theelimination of deviation was maintained to be not more than 0.02°. Onlyin Example 1-4, the removal was performed using the laser, whereas inthe other samples, the removal was performed using the ion implantationand the subsequent electrolytic etching. In the case where a preciseremoval method such as those described above had not been used,variation of not less than ±2° occurred already at this point of time.In the polishing for optical measurement, the removal using ionimplantation is more preferable because the degree of parallelizationdoes not need to be taken into consideration particularly; however, thedegree of parallelization is important in the present examples in orderto control to reduce the off angle variation.

For each of single-crystal diamond materials 20 obtained through theremoval, Table 1 shows: the state of the crystal defect points in themain surface; the number of the crystal defect line-like gatheredregions in parallel; the density of the crystal defect points; thedensity of the combined dislocation points; the number of thesingle-crystal diamond layers; the thickness of the single-crystaldiamond material; the off angle of the main surface; the concentration(average concentration) of the non-substitutional nitrogen atoms; theconcentration (average concentration) of the substitutional nitrogen;the concentration (average concentration) of all the nitrogen atoms; thetransmittance for light having a wavelength of 400 nm; and thetransmittance for light having a wavelength of 600 nm. Here, the stateof the crystal defect points in the main surface, the number of thecrystal defect line-like gathered regions in parallel, the density ofthe crystal defect points, and the density of the combined dislocationpoints were observed and calculated based on an X-ray topography imagefor the main surface. The off angle of the main surface was measured andcalculated by precise X-ray diffraction. The concentration of all thenitrogen atoms was measured by SIMS. The concentration of thesubstitutional nitrogen atoms was measured by ESR. The concentration ofthe non-substitutional nitrogen atoms was calculated from a differencebetween the concentration of all the nitrogen atoms and theconcentration of the substitutional nitrogen atoms. The transmittancefor light having a wavelength of 400 nm and the transmittance for lighthaving a wavelength of 600 nm were measured using a spectrophotometer.

Single-crystal diamond material 20 was machined into a shape of cutteredge, and was used to cut a workpiece for the purpose of evaluation ofchipping resistance. For a cutter, RF4080R provided by Sumitomo ElectricIndustries HardMetal was used. For a wiper chip, SNEW1204ADFR-WSprovided by Sumitomo Electric Industries HardMetal was used. As a lathe,NV5000 provided by MOM SEIKI was used. A cutting speed was set at 2000m/min, an amount of cut was set at 0.05 mm, and an amount of feed wasset at 0.05 mm/cutting edge. For the workpiece, an aluminum materialA5052 was used. After cutting the workpiece for 30 km, a chippingresistance evaluation I was performed based on the number of chippingsof not less than 5 μm in the cutter edge. Results thereof are shown inTable 1. In chipping resistance evaluation I, when the number ofchippings was not more than 1, it was considered as a usable excellentproduct. Moreover, a chipping resistance evaluation II was performedbased on the number of chippings of not less than 5 μm in the cutteredge after cutting a workpiece, which was aluminum material A5052, for30 km under conditions that a cutting speed was set at 2000 m/min, anamount of cut was set at 0.10 mm, and an amount of feed was set at 0.10mm/cutting edge. Results thereof are shown in Table 1. In chippingresistance evaluation II, when the number of chippings was not more than4, it was considered as a usable excellent product.

TABLE 1 Example 1-1 Example 1-2 Example 1-3 Example 1-4 Example 1-5Diamond Formation Method (Seed Crystal Type) HPHT (Type HPHT (Type HPHT(Type HPHT (Type HPHT (Type Ib) Seed Ib) Ib) Ib) Ib) Crystal Off Angleof Main Surface (°) 2 2 2 2 2 Load during Polishing (kgf) 10 to 20 10 to20 0.5 to 5 0.5 to 5 0.5 to 5 Selection for Polishing Direction duringPolishing Rotation→ Rotation→ Rotation→ Fixation Fixation FixationFixation Fixation Groove Formed through Existence/Non-Existence NotExist Exist Exist Not Exist Exist Photolithography Relation betweenGroove and — Parallel Parallel — Perpendicular Off Angle Width of Groove(μm) — 3 3 — 3 Interval of Groove (μm) — 200 200 — 200 State of CrystalDefect Points Points Points Points Interspersed Interspersed Gathered inGathered in Gathered in the Form of the Form of the Form of Lines LinesLines Density of Seed Crystal Defect Points (mm⁻²) 170 410 150 16 20Size of Diamond Seed Crystal (mm²) 4 × 4 4 × 4 4 × 4 4 × 4 4 × 4Thickness of Diamond Seed Crystal (mm) 1 1.6 1 0.8 0.7 Single- State ofCrystal Defect Points Groups of Groups of Groups of InterspersedInterspersed Crystal Points Points Points Diamond Gathered in Gatheredin Gathered in Material the Form of the Form of the Form of Lines LinesLines Number of Crystal Defect Line-Like Gathered Regions in 25 38 18 —— Parallel Density of Crystal Defect Points (mm⁻²) 1200 2500 1100 16 20Density of Combined Dislocation Points (mm⁻²) 400 1100 350 0 0 Number ofSingle-Crystal Diamond Layers 2 2 1 1 1 Thickness of Single-CrystalDiamond Material (μm) 1 0.7 0.6 0.5 0.5 Off Angle of Crystal Growth MainSurface (°) 2 2 2 2 2 Angle of Deviation from Parallelism betweenCrystal Growth 0.01 0.03 0.02 0.2 0.01 Main Surface and Main SurfaceOpposite to Crystal Growth Main Surface (°) Maximum Height Difference ofUndulation in Main Surface 0.2 0.3 0.1 0.05 0.05 Opposite to CrystalGrowth Main Surface (μm/mm) Arithmetic Mean Roughness Ra of Main SurfaceOpposite to 0.006 0.005 0.004 0.002 0.003 Crystal Growth Main Surface(μm) Concentration of Non-Substitutional Nitrogen Atoms (ppm) 35.0 51.531.7 0.1 0.3 Concentration of Substitutional Nitrogen Atoms (ppm) 0.60.5 0.3 0.3 0.4 Concentration of All Nitrogen Atoms (ppm) 35.6 52.0 32.00.4 0.7 Transmittance for Light having Wavelength of 400 nm (%; 8 6 9 6561 Conversion with 500 μm Thickness) Transmittance for Light havingWavelength of 600 nm (%; 53 45 48 69 68 Conversion with 500 μmThickness) Chipping Resistance Evaluation I (Number of Chippings) 0 0 05 4 Chipping Resistance Evaluation II (Number of Chippings) 1 1 1 12 8

With reference to Table 1, in each of Example 1-1 to Example 1-3, thenumber of chippings was low in each of chipping resistance evaluation Iand chipping resistance evaluation II because the concentration of thenon-substitutional nitrogen atoms was not more than 200 ppm, theconcentration of the substitutional nitrogen atoms was lower than theconcentration of the non-substitutional nitrogen atoms, thesingle-crystal diamond material had the crystal growth main surfacehaving an off angle of not more than 20°, and the groups of the crystaldefect points were gathered in the form of lines in the crystal growthmain surface that was the main surface. In contrast, in each of Example1-4 and Example 1-5, the number of chippings was high in each ofchipping resistance evaluation I and chipping resistance evaluation IIbecause the concentration of the substitutional nitrogen atoms washigher than the concentration of the non-substitutional nitrogen atomsand the crystal defect points were not gathered and were justinterspersed in the crystal growth main surface that was the mainsurface although the concentration of the non-substitutional nitrogenatoms was not more than 200 ppm and the off angle of the main surfacewas not more than 20°. Here, the crystal defect points were observed inthe crystal growth main surface, which was the outermost surface of thesingle-crystal diamond material, whereas the off angle was measured inthe crystal growth main surface at the initial stage of the growth. Thecrystal growth main surface at the initial stage of the growthsubstantially corresponded to an average surface of the crystal growthmain surface of 50% of the single-crystal diamond material at the centerthereof. The crystal growth main surface at the initial stage of thegrowth was calculated by determining a direction of inclination bymeasuring two cross sections substantially orthogonal to the crystalgrowth main surface by CL (cathode luminescence) in 1 mm at the centerof the single-crystal diamond material.

Although the crystal growth main surfaces of the present single-crystaldiamond materials were polished to be flat, evaluation results thereofwere the same values as those before the polishing. For each of thepresent single-crystal diamond materials, the ion implantation andelectrolytic etching were performed in the step of removing from thediamond seed crystal; however, there was no large difference inevaluation results when employing the method of slicing using a laser.In the method of slicing using the laser, after the evaluations,mechanical polishing was performed to form a normal flat surface andthen this plate was cut by a laser into a desired size, therebyobtaining a chip for a wire drawing die. Then, a wire drawing die wasproduced.

In the single-crystal diamond chip just before being formed into a die,the transmittances for light were measured; however, the transmittancesfor light were substantially the same as those in the case of thesingle-crystal diamond material. The transmittance of the die wasmeasured using a microscopic visible ultraviolet spectroscopyphotometer. The laser was employed to cut the main surface of thesingle-crystal diamond material strictly perpendicularly in the <100>direction, whereby the main surface of the single-crystal diamond chipcorresponded to (100). The wire drawing dies are provided with: holes (Agroup) formed by machining the main surfaces of the single-crystaldiamond chips strictly perpendicularly; and holes (B group) formed bymachining and angled off by 2° in a direction angled off by 2°. Becausethe off direction had been known in relation with the main surface sincethe synthesis of the single-crystal diamond material and the formationof the chip, a mark was provided to indicate the direction for thepurpose of alignment in the same direction.

As a result of evaluating five wire drawing dies of the A group and fivewire drawing dies of the B group, the axis of each of the holes of the Bgroup was off by less than 1° relative to the low-index plane with acrystal plane of (100) (variation in the axes of the holes was less than0.2°). The axis of each of the holes of the A group was off by less than3° relative to the low-index plane with the crystal plane of (100)(variation in the axes of the holes was less than 0.2°). Table 2 showsvariation in concentration of the non-substitutional nitrogen atoms ineach of the A group and the B group (variation relative to the averageconcentration). Moreover, Table 2 shows wear rate variation in each ofthe A group and the B group (variation relative to the average wearrate) and shows wear rate variation in the whole of the A group and theB group (variation relative to the average wear rate).

TABLE 2 Example 1-1 Example 1-2 Example 1-3 Example 1-4 Example 1-5Variation in Concentration of Non-Substitutional Nitrogen ±20 ±20 ±20 —— Atoms within Each of A and B Groups (Not More Than %) Wear RateVariation within Each of A and B Groups (Not ±2 ±3 ±2 — — More Than %)Wear Rate Variation within Whole of A and B Groups (Not ±4 ±5 ±4 — —More Than %)

With reference to Table 2, in each of Example 1-1 to Example 1-3, thevariation in concentration of the non-substitutional nitrogen atoms ineach of the A group and the B group was not more than ±20%, the wearrate variation in each of the A group and the B group was not more than±3%, and the wear rate variation in the whole of the A group and the Bgroup was not more than ±5%. All of these were small. On the other hand,in each of Example 1-4 and Example 1-5, a large chipping occurred.Hence, it was difficult to measure the wear rate variation in each ofthe A group and the B group.

In each of Example 1-1 to Example 1-3, since the variation among theangles of the axes of the holes was less than 0.2° as in the A group andthe B group, the wear rate variation was small irrespective of thedifference therebetween in the angle of each of the axes of the holes,i.e., 1° and 3°. However, in the whole of the A group and the B group,the variation among the angles of the axes of the holes was not lessthan 3°. Hence, it was found that the wear rate variation as a wholebecame large. This resulted from the off angle variation among thediamond materials in the first place. It was also found that when theoff angle of the diamond material was small, this variation can besuppressed readily. Moreover, it was also found that when the off anglewas small relative to the index plane of the main surface of the diamondchip, the variation among the angles of the axes of the holes becomessmall, which is more preferable.

Example 2

Single-crystal diamond materials of Example 2-1 to Example 2-12 wereproduced in the same manner as in Example 1 except for conditions shownin Table 3 and Table 4, and were subjected to chipping resistanceevaluation I and chipping resistance evaluation II. Results thereof areshown in Table 3 and Table 4. Here, for the polishing, attention waspaid to selection of polishing directions, and therefore Table 3 and 4show the polishing directions distinctively. “Rotation→Fixation” inTables 3 and 4 indicates a method in which a substrate made relativelyflat by a general method is polished for 2 hours while being rotated(turned) and then is fixed and polished for 1 hour. With this, defectsare likely to be introduced in the form of lines. “Fixation→Rotation”indicates a method in which a substrate made relatively flat by ageneral method is fixed and polished for 1 hour and then is polished for2 hours while being rotated. With this, defects gathered not in the formof lines are likely to be introduced. The loads during the polishing inTables 3 and 4 are loads in the case of “Rotation→Fixation” and“Fixation→Rotation”. Since the AsGrown surface of a substrate formed byCVD is smooth, single-crystal diamond materials can be grown thereonwithout polishing. Hence, an experiment was also conducted with regardto a diamond seed crystal not polished.

TABLE 3 Example 2-1 Example 2-2 Example 2-3 Example 2-4 Example 2-5Example 2-6 Diamond Formation Method (Seed Crystal Type) HPHT (Type HPHT(Type HPHT (Type HPHT (Type HPHT HPHT Seed IIa) IIa) Ib) Ib) (Type Ib)(Type Ib) Crystal Off Angle of Main Surface (°) 2 3 3 3 5 3 Load duringPolishing (kgf) 5 to 10 10 to 20 15 to 25 20 to 30 10 to 20 30 to 50Selection for Polishing Direction during Polishing Fixation → Fixation →Fixation → Fixation → Rotation→ Rotation→ Rotation Rotation RotationRotation Fixation Fixation Groove Formed Through Existence/Non-ExistenceNot Exist Not Exist Not Exist Not Exist Not Exist Not ExistPhotolithography Relation between Groove — — — — — — and Off Angle Widthof Groove (μm) — — — — — — Interval of Groove (μm) — — — — — — State ofCrystal Defect Point Points Points Points Points Points Points GatheredGathered Gathered Gathered Gathered in Gathered in the Form the Form ofLines of Lines Density of Seed Crystal Defect Points (mm⁻²) 1 3 21 21130 450 Size of Diamond Seed Crystal (mm²) 4 × 4 4 × 4 4 × 4 4 × 4 4 × 44 × 4 Thickness of Diamond Seed Crystal (mm) 1.6 1.8 3.2 3.5 1.7 3.5Single- State of Crystal Defect Points Groups of Groups of Groups ofGroups of Groups of Groups of Crystal Points Points Points Points PointsPoints Diamond Gathered Gathered Gathered Gathered Gathered GatheredMaterial in the in the Form of Form of Lines Lines Number of CrystalDefect Line-Like Gathered — — — — 23 95 Regions in Parallel Density ofCrystal Defect Points (mm⁻²) 2 22 90 310 1100 7500 Density of CombinedDislocation Points (mm⁻²) 0 5 22 80 320 2800 Number of Single-CrystalDiamond Layers 1 1 1 1 1 1 Thickness of Single-Crystal Diamond Material(μm) 0.6 0.7 0.8 0.9 0.8 1.1 Off Angle of Crystal Growth Main Surface(°) 2 3 3 3 5 3 Angle of Deviation from Parallelism between 0.01 0.010.01 0.01 0.02 0.03 Crystal Growth Surface and Main Surface Opposite toCrystal Growth Main Surface (°) Maximum Height Difference of Undulationin Main 0.02 0.04 0.05 0.05 0.4 0.6 Surface Opposite to Crystal GrowthMain Surface (μm/mm) Arithmetic Mean Roughness Ra of Main Surface 0.00050.001 0.003 0.008 0.007 0.006 Opposite to Crystal Growth Main Surface(μm) Concentration of Non-Substitutional Nitrogen 1.1 3.3 5.8 9.6 44.419.7 Atoms (ppm) Concentration of Substitutional Nitrogen 0.1 0.2 0.20.4 0.6 0.3 Atoms (ppm) Concentration of All Nitrogen Atoms (ppm) 1.23.5 6.0 10.0 45.0 20.0 Transmittance for Light having Wavelength of 5743 26 14 7 9 400 nm (%; Conversion with 500 μm Thickness) Transmittancefor Light having Wavelength of 68 64 58 53 48 45 600 nm (%; Conversionwith 500 μm Thickness) Chipping Resistance Evaluation I 1 1 0 0 0 0(Number of Chippings) Chipping Resistance Evaluation II 3 3 2 2 1 1(Number of Chippings)

TABLE 4 Example 2-7 Example 2-8 Example 2-9 Diamond Formation Method(Seed Crystal Type) CVD CVD CVD Seed Off Angle of Main Surface (°) 2 5 8Crystal Load during Polishing (kgf) 10 to 20 10 to 20 20 to 30 Selectionfor Polishing Direction during Polishing Fixation → Fixation → Rotation→Rotation Rotation Fixation Groove Formed Through Existence/Non-ExistenceNot Exist Not Exist Not Exist Photolithography Relation between Groove —— — and Off Angle Width of Groove (μm) — — — Interval of Groove (μm) — —— State of Crystal Defect Points Groups of Groups of Groups of PointsGathered Points Gathered Points Gathered in the Form of Lines Density ofSeed Crystal Defect Points (mm⁻²) 1500 2100 3100 Size of Diamond SeedCrystal (mm²) 4 × 4 4 × 4 4 × 4 Thickness of Diamond Seed Crystal (mm)1.6 1.6 3.2 Single- State of Crystal Defect Points Groups of Groups ofGroups of Crystal Points Gathered Points Gathered Points GatheredDiamond in the Form of in the Form of in the Form of Material LinesLines Lines Number of Crystal Defect Line-Like Gathered Regions in 120180 310 Parallel Density of Crystal Defect Points (mm⁻²) 14000 2500050000 Density of Combined Dislocation Points (mm⁻²) 5500 9600 23000Number of Single-Crystal Diamond Layers 2 3 3 Thickness ofSingle-Crystal Diamond Material (μm) 1.2 1.1 1.1 Off Angle of CrystalGrowth Main Surface (°) 2 5 8 Angle of Deviation from Parallelismbetween Crystal Growth 0.01 0.01 0.02 Main Surface and Main SurfaceOpposite to Crystal Growth Main Surface (°) Maximum Height Difference ofUndulation in Main Surface 0.04 0.03 0.4 Opposite to Crystal Growth MainSurface (μm/mm) Arithmetic Mean Roughness Ra of Main Surface Opposite to0.001 0.001 0.005 Crystal Growth Main Surface (μm) Concentration ofNon-Substitutional Nitrogen Atoms (ppm) 31.0 49.55 109 Concentration ofSubstitutional Nitrogen Atoms (ppm) 0.1 0.45 1 Concentration of AllNitrogen Atoms (ppm) 31.1 50.0 110 Transmittance for Light havingWavelength of 400 nm (%; Less than 1 Less than 1 Less than 1 Conversionwith 500 μm Thickness) Transmittance for Light having Wavelength of 600nm (%; 28 8 4 Conversion with 500 μm Thickness) Chipping ResistanceEvaluation I (Number of Chippings) 0 0 0 Chipping Resistance EvaluationII (Number of Chippings) 0 0 0 Example 2-10 Example 2-11 Example 2-12Diamond Formation Method (Seed Crystal Type) CVD CVD CVD Seed Off Angleof Main Surface (°) 17 3 3 Crystal Load during Polishing (kgf) 20 to 30Not Polished Not Polished Selection for Polishing Direction duringPolishing Rotation→ Not Polished Not Polished Fixation Groove FormedThrough Existence/Non-Existence Not Exist Not Exist Not ExistPhotolithography Relation between Groove — — — and Off Angle Width ofGroove (μm) — — — Interval of Groove (μm) — — — State of Crystal DefectPoints Groups of Groups of Groups of Points Gathered Points GatheredPoints Gathered in the Form of in the Form of in the Form of Lines LinesLines Density of Seed Crystal Defect Points (mm⁻²) 3500 230 200 Size ofDiamond Seed Crystal (mm²) 4 × 4 4 × 4 4 × 4 Thickness of Diamond SeedCrystal (mm) 3.2 0.7 0.8 Single- State of Crystal Defect Points Groupsof Groups of Groups of Crystal Points Gathered Points Gathered PointsGathered Diamond in the Form of in the Form of in the Form of MaterialLines Lines Lines Number of Crystal Defect Line-Like Gathered Regions in330 18 15 Parallel Density of Crystal Defect Points (mm⁻²) 50000 19001700 Density of Combined Dislocation Points (mm⁻²) 23000 850 600 Numberof Single-Crystal Diamond Layers 3 3 2 Thickness of Single-CrystalDiamond Material (μm) 1.1 1.2 1.2 Off Angle of Crystal Growth MainSurface (°) 17 3 3 Angle of Deviation from Parallelism between CrystalGrowth 0.03 0.01 0.2 Main Surface and Main Surface Opposite to CrystalGrowth Main Surface (°) Maximum Height Difference of Undulation in MainSurface 0.5 0.04 150 Opposite to Crystal Growth Main Surface (μm/mm)Arithmetic Mean Roughness Ra of Main Surface Opposite to 0.007 0.0030.003 Crystal Growth Main Surface (μm) Concentration ofNon-Substitutional Nitrogen Atoms (ppm) 190 24.8 21.6 Concentration ofSubstitutional Nitrogen Atoms (ppm) 10 0.2 0.4 Concentration of AllNitrogen Atoms (ppm) 200 25.0 22.0 Transmittance for Light havingWavelength of 400 nm (%; Less than 1 4 4 Conversion with 500 μmThickness) Transmittance for Light having Wavelength of 600 nm (%; 2 3838 Conversion with 500 μm Thickness) Chipping Resistance Evaluation I(Number of Chippings) 0 0 0 Chipping Resistance Evaluation II (Number ofChippings) 0 0 0

With reference to Table 3 and Table 4, in each of Example 2-1 to Example2-12, the concentration of the non-substitutional nitrogen atoms was notmore than 200 ppm and the off angle of the main surface was not morethan 20°. Moreover, the groups of the crystal defect points weregathered or gathered in the form of lines in the crystal growth mainsurface that was the main surface. Accordingly, the number of chippingswas low in each of chipping resistance evaluation I and chippingresistance evaluation II. Here, in each of Example 1-1 to Example 2-10,the single-crystal diamond material was removed from the diamond seedcrystal. Only in Example 2-11, the single-crystal diamond material wasnot removed from the diamond seed crystal, and the CVD diamond seedcrystal was not polished in the evaluation of Example 2-11. On the otherhand, in the evaluation of Example 2-12, the single-crystal diamondmaterial was removed from the CVD diamond seed crystal not polished. InExample 2-12, since the single-crystal diamond material was removedwithout polishing, undulation became large in the main surface oppositeto the crystal growth main surface.

In Example 2-13, synthesis was attempted to obtain a single-crystaldiamond material in which the concentration of the non-substitutionalnitrogen atoms was 250 ppm; however, a diamond material including notless than 15% of non-single-crystal diamond and non-diamond wasobtained, with the result that the evaluations in Table 3 and Table 4could not be performed. Therefore, it was also difficult to produce aperforated tool. In Example 2-14, production of a single-crystal diamondmaterial was attempted under the same conditions as those in Example 2-4except that the off angle of the diamond seed crystal was 25°; however,a diamond material including not less than 5% of non-single-crystaldiamond and non-diamond was obtained, with the result that theevaluations in Table 3 and Table 4 could not be performed.

Also in Table 3 and Table 4, the crystal defect points were observed inthe crystal growth main surface, which was the outermost surface of thesingle-crystal diamond material, whereas the off angle was measured inthe crystal growth main surface at the initial stage of the growth. Thecrystal growth main surface at the initial stage of the growthsubstantially corresponded to an average surface of the crystal growthmain surface of 50% of the single-crystal diamond material at the centerthereof. The crystal growth main surface at the initial stage of thegrowth was calculated by determining a direction of inclination bymeasuring two cross sections substantially orthogonal to the crystalgrowth main surface by CL (cathode luminescence) in 1 mm at the centerof the single-crystal diamond material.

It should be noted that in each of Table 1, Table 3, and Table 4 above,the expression “Groups of Points Gathered” indicates that the areas ofthe groups of the points are in contact with or overlap with oneanother, i.e., are connected to one another. The expression “Groups ofPoints Gathered in the Form of Lines” indicates that the groups of thepoints are gathered to be connected to one another in the form ofelongated lines. The expression “Groups of Points” refers to acollection of crystal defect points that are based on crystal defectlines branched from the same starting point. The expression “CrystalDefect Points of Seed Crystal” refers to a combination of startingpoints of groups of crystal defect lines of a single-crystal layer andstarting points of crystal defect lines that are not in groups. Theexpression “Gathered” indicates that 70% of all the crystal defectpoints in a specific range are concentrated in 50% of the entire area ofthe specific range. Here, regarding the specific range for the crystaldefect points, it is assumed that a range of one crystal defect point isa range having a radius corresponding to a distance to a proximalcrystal defect point. The expression “Interspersed” refers to a state inwhich there is no gathering defined as above.

It should be noted that for comparison, as Example 2-15, Example 2-16,and Example 2-17, type Ib single-crystal diamond materials each producedby the HPHT (high-pressure/high-temperature) method and a natural typeIa single-crystal diamond material were subjected to the evaluations inTable 3 and Table 4 above. Results thereof are shown in Table 5.

TABLE 5 Example 2-15 Example 2-16 Example 2-17 Method of FormingSingle-Crystal Diamond Material (Crystal Type) HPHT (Type Ib) HPHT (TypeNatural (Type Ib) Ia) State of Crystal Defect Points InterspersedInterspersed — Number of Crystal Defect Line-Like Gathered Regions inParallel — — — Density of Crystal Defect Points (mm⁻²) 15 10 — Densityof Combined Dislocation Points (mm⁻²) 0 0 — Number of Single-CrystalDiamond Layers 1 1 — Thickness of Single-Crystal Diamond Material (μm) 22 2 Set Off Angle of Crystal Growth Main Surface (°) 0 0 0 Angle ofDeviation from Parallelism between Crystal Growth Main 2 2 22 Surfaceand Main Surface Opposite to Crystal Growth Main Surface (°) MaximumHeight Difference of Undulation in Main Surface Opposite 80 30 50 toCrystal Growth Main Surface (μm/mm) Arithmetic Mean Roughness Ra of MainSurface Opposite to Crystal 20 12 14 Growth Main Surface (μm)Concentration of Non-Substitutional Nitrogen Atoms (ppm) 0 0 0Concentration of Substitutional Nitrogen Atoms (ppm) 90 200 1800Concentration of All Nitrogen Atoms (ppm) 90 200 1800 Transmittance forLight having Wavelength of 400 nm (%; Conversion 3 1 30 with 500 μmThickness) Transmittance for Light having Wavelength of 600 nm (%;Conversion 68 68 69 with 500 μm Thickness) Chipping ResistanceEvaluation I (Number of Chippings) 0 0 0 Chipping Resistance EvaluationII (Number of Chippings) 1 1 1

Example 3

For each of the single-crystal diamond materials in Example 2-1 toExample 2-11 in each of which the number of chippings was not more than1 in chipping resistance evaluation I, a diamond chip and a diamondperforated tool were produced to evaluate off angle variation and wearrate variation. Results thereof are shown in Table 5 to Table 7.Moreover, for comparison, each of type Ib single-crystal diamondmaterials each produced by the HPHT (high-pressure/high-temperature)method and a natural type Ia single-crystal diamond material wasemployed to produce a diamond chip and a diamond perforated tool, whichwere then evaluated in terms of off angle variation and wear ratevariation. Results thereof are shown in Table 6 to Table 8.

Hole axis and crystal plane orientation were confirmed and evaluatedusing X-ray diffraction with the chip being fixed to a mount such that aperpendicular direction corresponds to a direction in which a pluralityof outlines of the hole when viewed in the hole axis direction using amicroscope (outlines of the outermost circle in which the hole crossesthe rectangular parallelepiped of the chip, the innermost circle thatcan be confirmed as the minimum diameter in the hole, and the like) areconcentric. The evaluation with the X rays were performed in the samemanner as that in a general method of evaluating fluctuation, off angle,or pole figure of crystal of a plate-like single-crystal diamond. Sincethe perpendicular direction of the X-ray diffraction measurementcorresponds to the direction of the hole axis, the inclination angle ofthe hole axis could be confirmed by measuring the off inclination of thecrystal plane.

TABLE 6 Example 3-1 Example 3-2 Example 3-3 Example 3-4 Example 3-5Example 3-6 Example 3-7 Diamond Method of Forming CVD CVD CVD CVD CVDCVD CVD Chip Single-Crystal Diamond Material (Crystal Type)Single-Crystal Diamond Example 2-4 Example 2-4 Example 2-4 Example 2-6Example 2-6 Example 2-6 Example 2-9 Material (Example Number) ReferenceCrystal Plane (100) (100) (100) (110) (110) (110) (311) Orientation ofChip Designed Off Angle 1 7 10 0.2 0.5 20 0.5 between Chip Main Surfaceand Crystal Plane Orientation (°) Number of Cut Chips 6 6 5 6 6 5 6 OffAngle Variation (°) ±0.1 ±0.4 ±0.7 ±0.3 ±0.2 ±1.0 ±0.5 Variation in ±25±25 ±25 ±20 ±20 ±20 ±20 Concentration of Non-Substitutional NitrogenAtoms (Less Than %) Wear Rate Variation of Diamond ±1.5 ±2.8 ±3.0 ±1.5±1.5 ±3.5 ±1.8 Perforated Tool (Less Than %)

TABLE 7 Example Example Example Example Example 3-8 Example 3-9 Example3-10 3-11 3-12 3-13 3-14 Diamond Method of Forming Single-Crystal CVDCVD CVD CVD CVD CVD CVD Chip Diamond Material (Crystal Type)Single-Crystal Diamond Material Example 2-9 Example 2-9 Example 2-1Example 2-2 Example 2-3 Example 2-5 Example 2-7 (Example Number)Reference Crystal Plane (331) (111) (110) (110) (110) (110) (110)Orientation of Chip Designed Off Angle between Chip 3 5 2 0.5 3 5 2 MainSurface and Crystal Plane Orientation (°) Number of Cut Chips 6 6 5 5 55 5 Off Angle Variation (°) ±0.5 ±0.4 ±0.1 ±0.2 ±0.1 ±0.25 ±0.1Variation in Concentration of Non- ±20 ±20 ±30 ±30 ±30 ±20 ±20Substitutional Nitrogen Atoms (Less Than %) Wear Rate Variation ofDiamond Perforated ±2.0 ±2.5 ±1.0 ±1.5 ±1.5 ±2.0 ±2.0 Tool (Less Than %)

TABLE 8 Example Example Example Example 3-15 3-16 3-17 3-18 Example 3-19Example 3-20 Example 3-21 Diamond Method of Forming Single-Crystal CVDCVD CVD CVD HPHT (Type HPHT (Type Natural (Type Chip Diamond Material(Crystal Type) Ib) Ib) Ia) Single-Crystal Diamond Material Example 2-8Example Example Example Example 2-15 Example 2-16 Example 2-17 (ExampleNumber) 2-10 2-11 2-12 Reference Crystal Plane (110) (110) (110) (110)(110) (111) (111) Orientation of Chip Designed Off Angle between Chip 517 3 3 0 0 0 Main Surface and Crystal Plane Orientation (°) Number ofCut Chips 5 5 5 5 8 8 8 Off Angle Variation (°) ±0.25 ±0.8 ±0.1 ±3.0±5.0 ±2.0 ±22 Variation in Concentration of Non- ±20 ±15 ±20 ±20 ±70 ±70±80 Substitutional Nitrogen Atoms (Less Than %) Wear Rate Variation ofDiamond Perforated ±2.0 ±4.0 ±2.0 ±10 ±40 ±30 ±90 Tool (Less Than %)

With reference to Table 6 to Table 8, in each of the diamond chips ofExample 3-1 to Example 3-18 employing the single-crystal diamondmaterials of Example 2-1 to Example 2-12 in each of which the number ofchippings was not more than 1 in chipping resistance evaluation I, offangle variation was small (not more than ±1.0° in Example 3-1 to Example3-17 and not more than ±3.0° in Example 3-18) and wear rate variationwas small (not more than ±5.0% in Example 3-1 to Example 3-17 and notmore than ±10% in Example 3-18). On the other hand, in each of thediamond chips of Example 3-19 to Example 3-21 employing the type Ibsingle-crystal diamond materials each produced by the HPHT(high-pressure/high-temperature) method (Example 2-15 and Example 2-16)and the natural type Ia single-crystal diamond material (Example 2-17),off angle variation was large (not more than ±5.0° in Example 3-19, notmore than ±2.0% in Example 3-20, and not more than ±22° in Example3-21), and wear rate variation was large (not more than ±30% to not morethan ±90% in Example 3-19 to Example 3-21).

Moreover, based on the evaluation of the off angle variation and thewear rate variation in Example 3, it was found that a single-crystaldiamond chip having a main surface with a small off angle is suitablebecause wear rate variation due to wire drawing is small. Here, the offangle of the main surface of the single-crystal diamond chip coincideswith the off angle of the axis of the hole of the wire drawing dierelative to the crystal plane orientation. Basically, a single-crystaldiamond chip is obtained by perpendicularly cutting the single-crystaldiamond material, so that it is determined that a smaller off angle ofthe main surface of the single-crystal diamond material is morepreferable. However, it was sufficiently understood that when cuttingsuch that the off angle of the single-crystal diamond material differsfrom the off angle of the single-crystal diamond chip, the off angle ofthe single-crystal diamond chip, which is closer to the final product,has a larger influence. The off angle of the main surface of thesingle-crystal diamond chip was reflected to substantially coincide withthe off angle of the hole axis of the wire drawing die (perforated tool)relative to the crystal plane orientation.

The embodiments and examples disclosed herein are illustrative andnon-restrictive in any respect. The scope of the present invention isdefined by the terms of the claims, rather than the embodimentsdescribed above, and is intended to include any modifications within thescope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

10: diamond seed crystal; 10 c: conductive layer region; 10 dp: seedcrystal defect point; 10 dd: seed crystal dislocation point; 10 di: seedcrystal damage point; 10 dv: seed crystal chipping point; 10 m, 20 n:main surface; 20: single-crystal diamond material; 20 d: crystal defect;20 dp, 20 ndp: crystal defect point; 20 dq, 21 dq, 22 dq: crystal defectline; 20 m: crystal growth main surface; 20 r: crystal defect line-likegathered region; 21, 22: single-crystal diamond layer; 212 i: interface.

1. A single-crystal diamond material, wherein a concentration ofnon-substitutional nitrogen atoms is not more than 200 ppm, aconcentration of substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms, and thesingle-crystal diamond material has a crystal growth main surface havingan off angle of not more than 20°.
 2. The single-crystal diamondmaterial according to claim 1, wherein the crystal growth main surfacehas an off angle of less than 7°.
 3. The single-crystal diamond materialaccording to claim 1, wherein the concentration of the substitutionalnitrogen atoms is less than 80 ppm.
 4. The single-crystal diamondmaterial according to claim 1, wherein a concentration of all nitrogenatoms, which are a whole of the non-substitutional nitrogen atoms andthe substitutional nitrogen atoms, is not less than 0.1 ppm.
 5. Thesingle-crystal diamond material according to claim 1, wherein an angleof deviation from parallelism between the crystal growth main surfaceand a main surface opposite to the crystal growth main surface is lessthan 2°, the main surface opposite to the crystal growth main surfacehas an undulation with a maximum height difference Dm of not more than10 μm/mm, and has an arithmetic mean roughness Ra of not more than 0.1μm.
 6. The single-crystal diamond material according to claim 1, whereinin an X-ray topography image for the crystal growth main surface, groupsof crystal defect points are gathered, each of the crystal defect pointsbeing a tip point of a crystal defect line reaching the crystal growthmain surface, the crystal defect line representing a line in which acrystal defect exists.
 7. The single-crystal diamond material accordingto claim 6, wherein a density of the crystal defect points is more than2 mm⁻².
 8. The single-crystal diamond material according to claim 6,wherein a density of combined dislocation points of the crystal defectpoints is more than 2 mm⁻², each of the combined dislocation pointsbeing a tip point of a combined dislocation reaching the crystal growthmain surface, the combined dislocation resulting from a combination ofat least either of a plurality of edge dislocations and a plurality ofscrew dislocations.
 9. The single-crystal diamond material according toclaim 6, comprising a plurality of single-crystal diamond layers. 10.The single-crystal diamond material according to claim 9, wherein thecrystal defect line is newly generated or branched at an interfacebetween the single-crystal diamond layers, and a density of the crystaldefect points in the crystal growth main surface is higher than adensity of the crystal defect points in a main surface opposite to thecrystal growth main surface.
 11. The single-crystal diamond materialaccording to claim 6, wherein a plurality of crystal defect line-likegathered regions exist in parallel, and in each of the plurality ofcrystal defect line-like gathered regions, groups of the crystal defectpoints are gathered to extend in a form of lines.
 12. The single-crystaldiamond material according to claim 6, wherein the concentration of thenon-substitutional nitrogen atoms is not less than 1 ppm.
 13. Thesingle-crystal diamond material according to claim 1, wherein when thesingle-crystal diamond material has a thickness of 500 μm, atransmittance for light having a wavelength of 400 nm is not more than60%.
 14. A single-crystal diamond chip, wherein a concentration ofnon-substitutional nitrogen atoms is not more than 200 ppm, aconcentration of substitutional nitrogen atoms is lower than theconcentration of the non-substitutional nitrogen atoms, and thesingle-crystal diamond chip has a main surface with an off angle of notmore than 20°.
 15. A single-crystal diamond chip cut out from thesingle-crystal diamond material recited in claim
 1. 16. Thesingle-crystal diamond chip according to claim 14, wherein the mainsurface of the single-crystal diamond chip is a low-index planerepresented by a Miller index of not less than −5 and not more than 5 inan integer.
 17. The single-crystal diamond chip according to claim 14,wherein in an X-ray topography image for one of a crystal growth mainsurface and a main surface parallel to the crystal growth main surfaceof the single-crystal diamond chip, groups of crystal defect points aregathered, each of the crystal defect points being a tip point of acrystal defect line reaching one of the crystal growth main surface andthe main surface parallel to the crystal growth main surface, thecrystal defect line representing a line in which a crystal defectexists, and a density of the crystal defect points is more than 2 mm⁻².18. A perforated tool comprising a single-crystal diamond die, whereinin the single-crystal diamond die, a concentration of non-substitutionalnitrogen atoms is not more than 200 ppm, a concentration ofsubstitutional nitrogen atoms is lower than the concentration of thenon-substitutional nitrogen atoms, and the single-crystal diamond diehas a low-index plane represented by a Miller index of not less than −5and not more than 5 in an integer, a perpendicular line of the low-indexplane having an off angle of not more than 20° relative to anorientation of a hole for wire drawing.
 19. A perforated tool comprisinga single-crystal diamond die formed from the single-crystal diamond chiprecited in claim
 14. 20. The perforated tool according to claim 18,wherein in an X-ray topography image for a crystal growth main surfaceof the single-crystal diamond die, groups of crystal defect points aregathered, the crystal defect points being a tip point of a crystaldefect line reaching the crystal growth main surface, the crystal defectline representing a line in which a crystal defect exists, and a densityof the crystal defect points is more than 2 mm⁻².
 21. The perforatedtool according to claim 20, wherein a density of combined dislocationpoints of the crystal defect points is more than 2 mm⁻², each of thecombined dislocation points being a tip point of a combined dislocationreaching the crystal growth main surface, the combined dislocationresulting from a combination of at least either of a plurality of edgedislocations and a plurality of screw dislocations.
 22. The perforatedtool according to claim 20, wherein the single-crystal diamond dieincludes a plurality of single-crystal diamond layers, and the crystaldefect line is newly generated or branched at an interface between thesingle-crystal diamond layers, and a density of the crystal defectpoints of the crystal growth main surface is higher than a density ofthe crystal defect points of a main surface opposite to the crystalgrowth main surface.
 23. The perforated tool according to claim 20,wherein in the single-crystal diamond die, a plurality of crystal defectline-like gathered regions exist in parallel, and in each of theplurality of crystal defect line-like gathered regions, groups of thecrystal defect points are gathered to extend in a form of lines.
 24. Theperforated tool according to claim 18, wherein in the single-crystaldiamond die, the concentration of the non-substitutional nitrogen atomsis not less than 1 ppm.
 25. The perforated tool according to claim 18,wherein in the single-crystal diamond die, a transmittance for lighthaving a wavelength of 400 nm is not more than 60% when thesingle-crystal diamond die has a thickness of 500 μm.